Best small pet for young children. Hamster or gerbil?

Gerbils are brilliant and keep child friendly hours, unlike hamsters!
Keep them in a large, peat filled aquarium and you can see all their subterranean tunnels.
Socialise them well and they won’t nip.
Being desert creatures they get most of the fluid they need from the seeds and vegs they’re fed, so their litter doesn’t smell at all and needs changing relatively infrequently.
As you can tell, I was a big fan when my kids were little.
We did lose a clutch of babies when our first pair weren’t the requested females but a mixed pair and daddy gerbil objected…messy! Lesson learnt!

Guinea pigs are better than both.
Not nocturnal like hamsters, unlikely to bite, live longer, can be indoor pets if you have room for a decent sized run, which could be in a garage, on a landing or in a utility room, conversely can be outside but they love coming in for a cuddle, really appealing when they “chatter “
I can’t comment on gerbils but our “sweet” little hamster BIT, slept all day, was forever trying to escape and only lived to 18 months causing many tears from D2.

Gerbils are great with young children. We had them in two of our classrooms at school and they used to be handled daily, often running up someone's sleeve or performing silly tricks for chunks of apple. They're funny.
Hamsters bite, badly. And they sleep half the day. They're boring.

Hamsters are awake all night!

My Niece had one, many years ago, and it kept everyone awake whizzing round on its wheel all night. It wasn’t very friendly either

I love Guinea pigs but their house isn’t big enough. I had two rehomed gerbils and unfortunately the cat somehow managed to kill one of them when I bought them a bigger cage ( not sure how it happened but it was the brave cheeky one that died).