Any pet must be YOUR pet primarily and the kid gets to help.
I suggest fish. Like goldfish, which are fairly easy to maintain.
Reptiles often need special care and can carry salmonella. I had an anole as an adult and killed it by accident. I was never sure if it was the wrong cricket stuff or the wrong substrate or the wrong heat lamp, but he didn't last long.
Other small animals are not "easy", either. Small critters need more care than people think they do.
If you decide on something like a hamster or guinea pig, go to a rescue. Just take a look on Petfinder to see how many are abandoned or someone got two from a pet store and ended up with fifteen. Small critters need rescue, too.
I would not talk to a pet store about what an animal's needs are. I'd talk to a rescue - the people who have to clean up after the pet store gave a newbie bad advice.
I don't care if it's a mom and pop or big chain store. I've experienced serious problems with both and quit buying from a store. Years ago, I had a dwarf hamster develop diabetes (which they are prone to, something the mom and pop store we got them from never mentioned, and they also said we had 3 of a kind...we had two females, one male and ended up with a dozen babies).
If you get a critter like lizard or hamster or guinea pig, you should be willing to take it to an exotics vet if necessary and that's $$ just to get through the door.
Fish. Fish are good for kids, I think. Sorry about the slight tangent, but I feel strongly about the rap small animals get for being "starter pets."