We all brush our teeth together twice a day - DD2 (who is 16 months) doesn't really 'brush' either but over time, the older 2 have started to copy us brushing and they are actually getting really good at it even though they are only 2 and 3. All mine have gone through a chewing stage on their toothbrushes, but we don't push it or make a big deal of it. They love that we all brush our teeth together though it does get annoying at times (like if I want to be by myself when I brush my teeth, I can't, even if I try and hide in the bathroom and brush my teeth).