Can I actually afford it?

Flights are getting much more expensive. We just paid €600 for three basic Ryanair fights. Just return to England from Mainland Europe. In May. 2 suitcases.
Pre covid that flight would have been €200-250 max for the three of us. It’s the same non frills flight, same journey

Objectively you can afford it, plenty of people earning less do but it won’t be without some compromises. Your mortgage is not massive but I think you’ve been incredibly lucky with your childcare. £600 a month for two under school age is massively cheap. I am paying £16 a day 3-6 wrap around and £50 a day holiday camps so for three primary age kids you could be looking at more than you’re paying for nursery. Eg a week summer camp could easily set you back £750 for three. I also think holidays will end up being harder. My flights alone for August last year for 4 were £1800. I suspect you’ll hanker after something more than haven.

On activities, to an extent it becomes a choice but I don’t think you can assume you’ll limit to 2. Everyone I know does more than that. Something like brownies is cheap- for us it’s £50 a term- our most expensive thing is piano which is probably £1k a year in tuition per child.

A major consideration needs to be the children’s quality of life. We earn more than you but do not feel able to afford three children. I have two siblings, my husband has three. We spent a lot of our childhoods being told we couldn’t afford things or that we had to compromise due to the needs of our siblings. That isn't the life we wanted for our own so we’ve only had one child.

The finances can work. You make it work. It's that simple and those things you need to cut back on happen naturally. There are less of the 'first spends' as you naturally retain the baby items etc. But the costs come later, as they grow older and hobbies cost, university costs etc.
The question isn't always about money though is it? It's about the overall impact on life. Time available for three kids emotional needs as opposed to two etc etc.

People do go to canaries for winter sun yet. It can be lovely at 18-20 degrees to escape the dreary British winter. But it’s not pool and sea weather, they will be freezing. So Most families go later in summer as small children like beach and pools. In winter we have been, but to a 5 start hotel with indoor heated pool, and for hiking holiday. So it was no cheaper than summer tbh

Theres just so many expenses that children seem to need. We have had to pay privately for allergy clinic this month (€300 ish), Ds outgrown car seat (€200 ish). Last two months he need full replacement of most shoes as outgrown, for nursery he needs wellingtons and slippers kept there so x2 of those each time. He needs a new bike (even second hand cost) soon as outgrown, it will be a birthday gift, but even so, with three that would be birthday and Xmas gifts x3.

Last year we had sudden illness and then death of my grandmother, that involved last minute expensive ish flights back to uk and then accommodation for 10 days. Neither were expected so couldn’t plan for cheaper time. Ds just slept in our bed so we only needed standard hotel room, most have sofa bed for 1-2 also. And normal size hire car. If we had x3 teenagers We would have needed extra flight, larger hire car cost, larger suite or two hotel rooms. Easily €2000 extra.
I know this isn’t annually, but then the next thing comes up.

Our food probably costs us around €50 per person per week now ( about €150 total) In 10 years I imagine it will be €80+ due to inflation and child getting older. So with extra children, extra cost

Winter is fine for heated pool but they only tend to be heated until the end of April. There will be a few exceptions.

These are all "nice to have" but not essential things though?

I have 2 teens, their combined extra curricular activities cost nothing like £500/month.
A 12k flute I would imagine is not something many kids would have...?

DD has had 1 school trip abroad, I think it cost about £700. (She's year 13)
DS has not yet been abroad either school (he's year 9)

Even some places abroad can have cold pools then. Often places like Canaries heat pools until the end of April so pools can feel chillier in May. It all depends on how hardy your children are.

We carefully with May, pools can be cold and depending where you go the weather can be hit or miss. If your close to Scotland it is often cheaper to fly from there for the last week of August.

Lots of people don’t like to go away for the last week.

That’s odd. Was it late August?

I have one teen and they cost us a lot of money. I couldn't have any more dc but the older I've got the more grateful I am having 1. Within the past 6 months 3 parents I have known have died, one suicide, 2 RTA's. One family had 2dc, one 3dc and the other 5dc. One family for sure are having to sell the home and downsize. Not sure about the others. You never know what's around the corner (not just death but divorce or having a child with medical or SEN meaning one parent has to stay at home). I know that both myself and dh could support our dc individually without having to move house or it having a significant day to day financial impact.

We have a household income of £110k and no mortgage.

I have three. They are 19,17 & 15 now. Three kids is expensive. All deals seem to be for families of 4. The extra bedroom in the villa, the extra plane seat, the extra birthday, school trip, driving big lessons, car, university costs... 3 is a lot. It's not just about what they cost when they are little.

Not for me.
We have one , and I’m not sure we will have a second. Time and Money are both factors.
We earn well, but things are getting ever more expensive and I imagine will just keep increasing the next 5,10,15 years. I don’t want to always be playing catch up.

Time is the biggest issue. Dh works full time, I work part time ( with some full time weeks). Even with 1 child who doesn’t no extra activities yet it’s still a lots of things to make time for. school events, appointments, illness. all times by 3.

If one child has parents evening appointment, and another a sports event with school other end of town, and other sick with chickpox your just stretched very thin with only two parents and 3 children. With 2 children at least you can tag team when needed.

We don’t buy things for the sake of it either. But basics like our mortgage rate increased ££, food prices have gone up, utility prices etc. our monthly basic costs are much higher than 5 years ago without us changing anything. Ie we use less electricity that we did 5 years ago, but monthly now costs €50 more.

Well, no, but DS doesn't want to go to uni for the sake of it - he wants to go because he's academically very able, and wants to experience studying a particular subject in greater depth, and so that he can then go on to work in in a particular field.

We have 2 home offices and they are 100% needed now. Couldn't run either of our jobs from the kitchen table, and nor would I want to. It's a big consideration for house viewing now and basically means we can't move as would need to be looking at 6 bed houses to improve on what we have (bought as 4+study)

I'm budgeting at least £6k/year parental contribution for DS when he goes to uni (according to the MSE calculator).