I started when the first tooth appeared mainly just to get the whole routine rolling. My DD has hyper-plasia where her teeth (her front top and bottom ones, 4 in total) are missing some of the enamel and are brown, it looks like they are rotten but they aren't. The dentist recommended I put toothpaste on her teeth after brushing too to help with the hyper-playsia. Anyway, my point is that it seems to be new that it's not really necessary for kids to spit toothpaste out, apparantly it is better for their teeth if they don't. I have always encouraged them to spit (harder than it sounds!!) but I always get some water and kinda rinse it out for them.