We have a Labrador that we got when ds was 9.
There is no way I would get a puppy with 3 such young children.
The first few months they are essentially baby crocodiles. ds did not enjoy the puppy phase as they are heavy and strong as puppies and those baby teeth are sharp!
They continue teething until they are around 18months and are well known to be chewers until then. That means you can never leave anything within their reach - toys, shoes, books or they will become chew toys for them. Ours even chewed carpets and sofas overnight.
If you get a boy you should not neuter them until they are a minimum of a year old, preferably longer, it will be at least 29kgs by this stage and will try to hump your children constantly. Being a big dog they could end up with accidental scratches from their nails which can scar.
Labradors in particular are food bins and need good consistent and repeated training not to eat anything that is not given to them (and not to sit, stare and drool at you while you are eating!). Your kids should not eat walking around near them.
You should not leave your young children in the same room as such a big dog unsupervised.
Be prepared for a complete shedding twice a year where you will need to vacuum at least twice a day. If you have never owned a Labrador you don't know how bad it can get, and it lasts weeks!
The dog will need good long walks every day in all weathers or they will become destructive.
My BIL/SIL underestimated the amount of daily training you need to put in with a puppy, dogs need to be trained or they will be a problem, especially with children. They PTS their spaniel last week after bit one them. Even more importantly, your children need to be trained too, how to approach a dog and moderate their behaviour around it, honestly your children are too young for that, and the consequence of getting it wrong are high for your children and the dog.
Saying all that, they are the best dogs in the world! (I would say just not yet for your family)