I have heard they usually start around two. However, the dentist will probably reccommend that you also brush them. It is a good lesson in taking turns also!
Yeah, I definitely am a proponent of kids learning how to take care of hygiene as early as possible. But, I do think parents need to go behind them and make sure they get all of their teeth clean. Sort of like with seatbelts; I always let the kids do them, but I also check to make sure it's done properly.
Both mine started to want to do it around the age of two. So we take turns on who goes first. First we will brush our own teeth, then we brush each others teeth. They thought it was way cool that they got to brush mommies teeth that they didn't realize I was brushing theirs. Usually by the age of 5 they are good to go on their own!
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"We Need more Monkeys!!"
My dentist told me to take care of it until they are six. However, as soon as they show an interest, I always let them start and then I finish it up for them.
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Old Glory