i like rain have had a few cats in my time all from kittens and no they are not hard to train and rains right they do grow with the children
kittens are very playfull as well as they grow they form there own personalties and i dont think two cats are the same, if you start of as you mean to go on with a cat deciding if its a house cat or indoor and outdoor cat ours used to come and go as they please through a cat flap

i also tried hamsters but i found children do get fed up with pets after a while so make sure its something that you will want around as well
what rain says about dogs is right also we had a jack russel and he was into his barking and my children were older but he would still nip at them if they anoyed him

large dogs need a good walk or a large garden to get pleanty of excersise
you should be able to get lots of info from your local shelter