I, too, am having this problem with my 28 mo. She simulates spitting, but I have never seen anything come out. Perhaps it is because I am still using a pea sized bit of toothpaste. I know she knows how to spit, because she enjoys making little spit bubbles a lot (Oh, joy), but I can never seem to translate that to the teeth brushing thing. So, I suspect this is a common problem. It's kind of a weird use of muscles for them to master.