To buy a buoyancy aid instead of a life jacket?

I wouldn't claim to be an expert, but we sail, and we wear lifejackets on the boat when falling in the water is very much not supposed to happen. Though in fact in bad weather we have always insisted everyone is in a harness and clipped on as picking up a man overboard is pretty difficult and it's much better not to go in in the first place! But for anything like dinghy sailing or windsurfing where getting wet at some point is almost inevitable then we have always worn buoyancy aids and I have never seen anyone do otherwise.
A life jacket is only of use if it's inflated and as others have said, it's not designed to really swim in. Trying to right a dinghy and get back in it with an inflated life jacket on would be a nightmare and I imagine it would be the same paddleboarding. Not to mention the fact that you'd need a large supply of life jackets or be willing to spend a long time deflating and fitting a new CO2 cannister every time someone fell in in a self inflating lifejacket. And I agree with the PP who said that you do need self inflating for kids. I have a self inflating one myself now after I did a training exercise and discovered just how difficult it is to find and pull the toggle when you are sinking in freezing cold water and I wouldn't expect a child to manage that.
For an activity where you are likely to fall in but not be very far from your boat/board and need to swim back to it then I'd say a good quality buoyancy aid is the right tool for the job. Just make sure it's the right size, and personally I always prefer those straps between the legs. One of my DS's is very thin and once when we were wearing hired buoyancy aids on holiday his shot right over his head when he capsized as there were no leg straps. When our kids were little we had the buoyancy aids with collars to make sure their heads were supported but if I recall rightly the normal ones were OK from about age 5 or so.
But the first rule of water safety is really to avoid having an incident in the first place so I'm glad to see you've reconsidered your plans somewhat OP. Sticking to lakes for your paddleboarding sounds very sensible, though don't get complacent. There were several deaths last year on one of the lakes we go to regularly because people thought "it's only a lake" and went out poorly prepared.

Whatever you do, please make sure it's rated correctly for their weight. I naively bought a buoyancy aid for my DD1 at a supermarket when she was young. It completely tipped her face down in the swimming pool. She couldn't move. It was incredibly scary, even though we were only a metre or so away. We had to lift her out of the water. I'm sure it was a very effective aid but it was just too buoyant for her body weight.

If you’re down on the Atlantic coast, Biarritz area, I would take lots of care and caution over which beaches you pick. Many are entirely unsuitable for children (and intermediate adult swimmers) due to the strength of the current and waves.

I’m from the area and every year there are tragic deaths. I don’t want to spoil your plans, but just advise you to take care.

A good buoyancy aid is required for supping. Go for a good brand, like palm and make sure it is correctly fitted and adjusted However you'll probably only be able to paddle on the sea if it's flat or upto about 1ft and in very low wind and preferably onshore. I get out on the sea once in a blue moon because it's rare to find the right combo of conditions on my local beaches.

You might be better off doing body boarding.

oh and whatever you get, get them in a bright colour!

no need for such an arsey response

the whole point is that different supports are better for different scenarios which is exactly what OP is asking.

In the paddleboarding incident last year in Wales, for example, 2 of the people who survived WEREN'T wearing any sort of buoyancy aids or life jackets at all, and those who died WERE - because essentially those without were taken under the water and then came out in a calmer part of the river where they could get out, but those wearing them kept being pulled up so couldn't escape.

Having done a lot of SUP-ing and being chest heavy I find it really hard to get back on with any sort of aid or jacket around my top so in some conditions I would be safer not wearing anything so I could get back on the SUP easier (I still wear a belt etc, and wouldn't recommend this for kids).

OP, sometimes people get confused and think buoyancy aids mean armbands or something - as long as you mean the jackets then I think they are completely fine and better for what you'll be using them for - the main advantage of lifejackets is the way they will keep you face up if unconscious - presumably the aim will be to stay on the boards so you just want something that will help the DC float for a few minutes if they do fall off while you get them back on again. There's no point in them having lifejackets that they can't actually move their arms sufficiently in. Most buoyancy aids are VERY buoyant, thus the name, it's not like they aren't as "good" as life jackets, they just balance you differently. For what you want to teach the DC (actually using the boards and ideally self-rescue) they are much better than lifejackets.

My dc had buoyancy aids for bodyboarding when young though, worked well

A buoyancy aid will support your weight in water (if correctly sized) but it won't support the person in a life saving position and in some instances, can flip someone face down. They work if someone enters the water alert and not injured

if the surf is too big for a reasonable swimmer to safely swim in then it isn’t safe to swim! For water sports (in deeper waters) you need life jacket but I don’t think sup is going to be possible if people are surfing

There is a lot of misinformation on this thread. For a normal weight adult, a 50N buoyancy aid will completely support your weight in the water. You don't need to swim. You only need to be conscious so you can hold your head up. Buoyancy aids are what people wear for kayaking, SUP etc because they allow you to move freely and the chances of being unconscious in the water are low (a trade off of risks). A children's buoyancy aid will do the same thing for them IF you get a proper one. Look for brands sold in outdoor shop in the UK.
A lifejacket supports an unconscious person in the water. It is overkill for SUP for adults.
What you choose for your children is your call.

At that age, they would need self-inflating life jackets, which would inflate every time they hit the water. Life jackets are bulky and difficult to do anything other than doggy paddle. Buoyancy aids are just that - aids - they will not support staying alive.

I would wait until they get an opportunity to do SUP somewhere with no waves. It’s hard enough to master on flat seas.

Boogie boards, in the swimming zone, with you and a life guard keeping watch, would be a much more fun option at that age. They can stay in their depth and have the fun of successfully catching waves, rather than trying to master SUP under difficult and possibly dangerous conditions.

Just to add - local knowledge as to sea conditions is always best so I would check with local lifeguards/coastguard etc as they should know rip/tide/current/wind conditions at given times and would be better placed to advise as to safety in the water.

The fact you're inexperienced enough to be asking this question shows you absolutely shouldn't be taking a 7 year old to this activity, you don't sound responsible enough to supervise.

Finally someone that actually knows what they are talking about! Lifejacket use is very rare in watersports. Almost all people that go paddleboarding use buoyancy aids. Nobody swims in a lifejacket! There are huge variations in how big and bulky a buoyancy aid can be. I wouldn't put my kids in a lifejacket in a surf beach, but to be honest, if things are that dangerous there, I wouldn't let them swim there either.

I don't think paddle boarding with children in waves is ideal. Generally you would want to do it in relatively calm water in which case, bouyancy aids are adequate.

Life jackets aren't a swimming aid but are rescue equipment and not really suitable for swimming or paddle boarding. They can impede getting back on the board and they impede swimming. It's different if you're on a boat and the expectation is that you WON'T enter the water but where you're intending to enter the water I would ensure that safety is considered firstly in terms of the water itself being safe and suitable for the planned activity and then any safety devices are considered in the context of how they would be used.

I mean, they are two different things.

Buoyancy aid is just that, it helps negate the weight of clothing you are wearing. Typically you will still need to swim/ tread water to keep properly afloat.

A life jacket will keep you afloat without effort but as such is bulkier and more designed for when you are going to be rescued back into a boat, rather than swimming any great distance.

Honestly, if you don't know the difference between the two I'm not sure it's especially wise to be thinking about open water swimming/ SUP, unless you are doing it under supervision in which case any reputable company/ instructor will provide you with suitable equipment anyway.

They are life jackets not bouyancy aids.

A life jacket is designed to turn you onto your back so the only swimming you can do unless you are very strong is on your back. Bouyancy aids just help you float.

Presumably it is lifeguarded? I would say lifejacket when on a board. If there is a swimming zone I think an adult close by is more important than a bouyancy aid.

Well, i wouldn't be letting 7 & 10yo's go paddle boarding in the sea in those conditions at all & as you haven't got the kit, this will all be new to them?

Life jackets are bulky and will make mastering a SUP harder, so a buoyancy aid is best but in a safer life guarded area with an instructor, such as a shallow in land lake.

I assume you don't mean proper bouyancy aids with a gas cannister and a toggle you pull to inflate? If you mean a floaty jacket for use in swimming pools, then no. Take the advice and get life jackets that are the right size for them. They're not designed to swim in, they're designed to stop you drowning.

How well can they swim? If they can swim properly then it would never occur to me to put a life jacket on a child swimming off the beach. Swimming in a life jacket is bloody hard work. If they can’t swim well enough then they shouldn’t be in the water beyond paddling about. On the SUP I’d put them in full life jackets if there are currents but have them try them on if you can. Some are a lot more comfy than others.

Life jackets all day long when in the sea, in my opinion.

A buoyancy aid is to aid you when treading water and most, if not all, don't have the required buoyancy to carry the weight of a person if they aren't able to tread water. Not as big a concern sometimes but when dealing with the ocean and currents I'd prefer a life jacket for my kids.

Surely there are two separate needs here. If doing a water based activity like sailing or SUP where you expect to be out of the water for it but there is a chance of falling in or capsizing then a life jacket. If not strong swimmers then buoyancy aid to help keep afloat whilst swimming. However I would really consider whether these are the correct beaches to do either activity especially if the kids are not strong swimmers, with or without buoyancy aids etc. Or at least try it out with an organised group where all equipment and training is provided plus a qualified instructor to supervise and help, on a suitable stretch of water.