Labs are known to have hip displaysia issues, as well as other large breed dogs. Research really does need to be done to choose a pet that suits your family situation.
I actually adopted my lab from a family who had a 2yo child, and the kid loved him, but the lab was just to boistrous to be left alone with him and knocked him over etc. With that being said, I dont think they ever took him for walks, or played with him and showed him any affection, so as soon as they went outside, he got excited. He is much older now and still gets excited and could easily knock small kids down, but he doesnt jump and he is very gentle and kind and settles down when we tell him. He will go collect a ball and just drop it in from of them til they play with him!! A 10yo old girl looks after them for us when we go away for weekends etc and she is fine with all 3 of them! She will feed them and play with them to exercise them rather than walking them as walking all 3 is a very special talent! Haha.
There is a huge amount of responsibility in having a dog, but they are best friends for life. We buy ours fresh meat each week and cook them rice and pasta, we spend a fortune on toys for them for them to tear them apart only minutes later. You need to walk them, play with them, train them, bath them, clean up after them, take them to the vet, socialise them with other kids and dogs, show them affection etc.
But... they are well worth it and we wouldnt have it any other way!