I'll have to try that experiment with my 15 month old. He's spent a lot of time on the keyboard, and he and I played with the sampler, but I didn't have him try the drums.

I didn't notice any lag, but maybe that's because my son can't stop himself from making the app go away: the home button is too irresistible. Someone needs to come out with a slip case that makes the home button unreachable.