I like the lizards, it's like having pets that you don't have to feed
The only thing that can be a bit annoying with them is that they poo everywhere but so long as you always wipe the kitchen surfaces in the morning before you use them and check cups and plates for poo (they get in all our cupboards), then it's not too bad.
As SMS says, they eat bugs and I'd much rather have geckos than bugs around the place
Your 4 year old may well run around after them but I doubt he'd catch one, they're fast and they run as soon as they see you or if you turn a light on.
we live in an old place and we don't really get that many of them - I think they must be territorial because I've seen a bigger one scaring off a smaller one before now, so the ones you do get in your place could possibly be the same ones that have lived there for ages.