I got my first dog when my kids were 6 and 8, so he was bought up with them, as well as having lots of their friends visiting, he also came from a breeder with young kids. He is still not a natural lover of young children, though obviously is used them and is gentle. I do sometimes shut him away for peace and quiet if we have young kids visiting

Lillie is fine with little kids (as above, though my kids were 2 years older when she arrived) she mostly ignores, or tolerates them though.
Teva, my youngest dog has been bought up with my, now, teenage kids. We do still have visiting little children, and she absolutely adores them. She would if she was allowed to, make a beeline for any little people we see out and about. She is incredibly gentle with them and obviously loves being aroung them!
Imho as well as carefully socialising your dog around kids, it is equally important not to let kids annoy/space invade the dog
