i know this is an older post, sorry.
my dog was 6 when i adopter her. she's a german shepherd mix, so there's surely breed differences. she's around kids all the time; however, i don't have any of my own. the thing i most appreciate about her is that she's patient with kids, even really young ones. if she's annoyed by a little kid, she'll get up and move somewhere else, but she'd never lash out at one.
i think i would prefer to introduce a child to an older dog rather than a younger one because younger dogs tend to have more energy and are more likely to jump on/knock over small children. that, or play a little rough. i think it's a definite benefit that these labs were raised around children - i say, go for it!