Guinea pigs are a lot of work for little return as far as human playtime goes. We went thru the small animal stage here, gps, frogs, hermies, betas, baby sat a snake and a lizard and all I have to say is, done. If I have to put in the work, I want the snuggle time.
Some people are fine with the small pets, or have space/time constraints. I happen to prefer to have dogs and cats, they are just more hands on, especially for a little child. GPs and the like are pretty fragile, and so darned cute a little kid could just want to squeeze the bejesus out of them, that doesn't end well.