I let my girls brush their teeth in the bath. Whilst my 17 month old doesnt effectively 'brush' , sucking on the brush and moving it around her mouth has given her an idea of what to do. I have noticed in the mornings when all 3 of us brush our teeth, she watches me do it and then brushes correctly - imitation is the key i suppose.

We also make it a fun thing...and those dreaded mornings where my morning coffee has not set in yet, my 3 year old will remind me ; "mumma, we havent brushed our teeth !!!".