I had hamsters when I was a teenager. They can be fun, but not something I'd recommend for small children. They can bite if they're not socialized or just feeling grumpy, and they're nocturnal, which means squeaky hamster wheels throughout the night
We recently bought our older daughter a small tank with two fish and a snail. The fish both died shortly after and she was heartbroken, but Sid the snail is still thriving!