My then 5 year old was a self-proclaimed "bug expert". The house was full of jars with dying bugs in them (he was supposed to let them go, but often forgot), he rescued worms, one day he came in with a cup full of maggots that he picked off a dead squirrel ("awwww, awwww, look at the baby worms!") , and he desperately wanted a pet of his own.
At the time I got them, we had 3 dogs who weren't particularly fond of children. So, no room in the family for another kid-friendly dog. Pocket pets (hamsters, etc...) were just a little too fragile for a 5 year old and a 1 1/2 year old. Fish can't be held. So, I found him a pet that fit his interest and that he could actually hold and play with.
He _LOVES_ his hissers! They were the absolute perfect first pet for him. He can play with them, and it's not a huge deal if they get dropped - although we would not tolerate purposeful cruelty, not that he's ever tried it.
So that's why I have a 20 gallon tank of hissers in my family room.
We do have a rule that he's only allowed to play with the boys outside of the tank. They are a neat pet, but I don't particularly want a colony of them in my walls. My son has the attention span of your average gnat, and I have found hissers around the house.
We've had them about a year now. He still loves them and plays with them regularly. They are an awesome first pet!