I have rehomed dogs with young kids, one a baby,,,,,,,,,,,,,,,,,, but they are few and far between, if you look at rescues, try to find the ones that use foster homes, I have been bitten badly twice, both times by dogs we had been asked to take on from other rescues that had been fine in kennels but turned into unpredictable monsters in a home environment.
I would agree that a lab maybe be too big for young kids in my experience younger ones are daft and bouncy, a smaller Heinz 57 maybe better.
Just one thing, I once went to homecheck a young family who were adamant they wanted to rescue a springer, took one of my dogs, and although their kids were ok with dogs out and about at a distance, the eldest who was about 4 was very frightened of Meg close up, and wouldn't come anywhere near her, in this case a puppy was suggested,
Have a look at Dogpages forum lots of rescues on there that use foster homes and will rehome to kids