I have had a few dogs in my life and currently have a 4 year old show cocker.
Having a dog is hard work. It's hard with a puppy and it does get easier with time, but it never becomes super easy.
Rescue dogs can have issues that need work too, so they are not guaranteed to be much easier than a puppy. They may not come fully trained - and an un-trained dog can be hard to have around.
Getting a dog means having to adapt your life to suit the dog. Put harshly, if you're not willing to do that, don't get a dog.
You need to make time for the dog every day - not just to give it a few walks, but it needs to be around you. They are sociable animals.
There has to be a plan for what to do when you want to go on holiday, if you're going to the hospital or have long days out. Or if something else happens in your life.
I walk my dog every 4-6 hours, although she does sleep well at night. Some of the walks might just be 10-15 minutes long, but at least one will be 30-45 mins as a minimum and includes training and playing. My dog isn't massively demanding regarding exercise.
With fairly young children, it's also worth considering that an older dog might not enjoy being around them all the time. The older my first dog got, the more he just wanted to be left alone and not have to deal with children.
A younger dog can get enough of it too, so I'd always say to keep a constant eye on dog and children when they are interacting.
You need to factor in the cost of insurance, unexpected costs, worming and flea products, time for grooming (or get a groomer to do it which can be often and £20-50 per time), lead, toys, bed, food, poo bags and so on.
Sometimes the dog gets ill and has to get treatment - it can be easy or hard depending on the dog - the dog may not like getting ear or eye drops.
The dog may get tummy issues which will require washing the dog and cleaning up after accidents inside the house. You need to pick up after the dog generally anyway, but when the dog has tummy issues, it isn't fun.
They can be disgusting - rolling in all kinds of stuff, walking around in stinky mud, eating all kinds of horrible stuff.
A dog generally doesn't care about the weather, and will need a walk to get the doggy facebook updates and do his/her business, no matter if you're ill, cold or tired. If the dog needs to go out in the middle of the night, you can't ignore it. Walking is nice when the weather is nice, but it can feel really frustrating when the weather is awful. Add tummy trouble to that, and it can feel even worse.
It's hard work, but if you're willing to do it, then it's worth it.