Just to add to the good advice here...
I had a lot of worry with our rescue pup (5-6 months when we got him) and children, in the first year or so after we got him. He started off very submissive, but as he got 'safer' with us he got braver - and adolescence kicked in, of course.
We had episodes of growling or even snapping to warn kids away from him when in his bed, from him if chewing bones or chews, etc. Not just kids, either! But it was all guarding, or fear - he needed space to get used to people, and trusting them.
Wasn't ideal for a family dog, really, but we got a wonderful behaviourist in who sorted us out. We learned to warn all visitors to leave the dog alone, till he got to know them. We made sure he had safe areas where NO kids, or adults, were allowed to disturb him. We never gave him bones or chews except when he was alone in the garden, or in his crate. And we gave visitors treats to feed him at random intervals. The stair gate went back up, so kids could be free of dog upstairs.
All worth it. Mouse is now well over 3 years old, affectionate, and absolutely lovely. I still wouldn't let a child stroke him when he has a chew, he still has his bones outside when we're not using the garden, and he is never disturbed in his bed. Thats just respect, I think. There was a fair bit of child/visitor-training involved, as well as dog-training, but it was needed - poor old pup had trust issues, unsurprisingly, having had a duff start in life.
Adolescence passing makes a huge difference, too!