The expert said kids should brush their teeth when they have teeth. My experience :
My daughter is 2y11m now.
-When she had 4 teeth (around 13 months), I used wet cotton pad -- of course drinking water to clean her teeth & tongue. She love it very much.
-When she was 2y, I taught her to brush the teeth by herslef, no need for me to re-brush becauce she clean very well. Sometime, she was lazy & don't want to brush, let her bite the cotton pad or feed her with water.