I don't recommend chinchillas for most kids because they are very easily stressed animals. Most of them don't tolerate much handling, and they need a very quiet environment. Plus, the vast majority of them remain somewhat skittish throughout their very long lifetime and never seem to warm up to being handled. (I know there are exceptions, I said the majority)

I would recommend a pair of rats. You can't get much more smart, loving, and interactive in a small package than a rat.