Most cats like companions and some don't so much. Either way cats have a hierarchy system and work it out for themselves. My parents have had cats that don't get along, but tolerate each other. Currently they have two young'uns who play together, sleep together and play fight together. Frodo (the eldest of the two) can play rough, but Billy (younger) just gives it straight back
I really can't see a problem unless your 5yr old is a complete nutcase. And he doesn't sound it.
If you've fallen for the kitten I'd go for it
