Oral hygiene starts with the pregnant mother. Studies have shown that babies from mothers with a good oral hygiene grow stronger. Considering the amount of sensitive surface we have in our mouth and the effect an inflamed surface has on the immune system this seems quite understandable (see Why brush my teeth).
After birth oral hygiene of both parents becomes important as there are many chances they could pass on their oral flora onto their child. A spoon shared with the child, a pacifier cleaned in the parents mouth, there are many things we share with our kid. In these situations we pass on part of our oral flora, and it can start to grow and multiply in their mouth. While parents should avoid sharing their flora with their kids, in reality it is something we do not or cannot always avoid, so a perfect oral hygiene is a choice children can thank them for.
Parents should start brushing their children's teeth from the very first tooth on. The reason to clean baby teeth is not only the teeth themselves, but preventing an oral flora to grow that is bad for their final teeth.
As more teeth come in you can start flossing early, that way your kid get's used to flossing and it becomes a common part of oral hygiene.
Since the big goal is to get our kids to continue brushing when they are on their own, it's a good choice that they build up a healthy relationship to brushing and flossing their teeth. You can give your kid a children’s tooth brush to play early. Some parents give their kid one as early as for the first birthday. The kid can use it and try to brush along when the parents or siblings are brushing their teeth. That way it become a playful and chosen act to the kid.
When you kid starts developing a good hand coordination, latest when he/she can draw a circle, typically around age 5 or 6, your kid can start to learn brushing (see Learning to brush).
Once your kid is brushing their teeth perfectly the parents can stop the post-brushing. If you build up the right attitude in your kid, he/she hopefully continues to brush his teeth carefully and at all appropriate times (see Some Timing Tips).
Once all teeth are at least 4 years old – typically around age 16 or 17 – the biggest cavity risk is over. If you came so far cavity free all you have to do is continue brushing and flossing.