More than a fifth of pre-school kids already have cavities.
Experts say that's because parents give their kids exclusive control of the toothbrush far too early.
Four-year-old Leanna Holden knows when to brush her teeth…
Leanna, 4, "Morning and night."
But does she know how?
Dr. Claudia Tomaselli a pediatric dentist says, "Hold you toothbrush real good, brush right in circles over there .You would be surprised how a six-year-old still doesn't have the dexterity to get all in the nooks and crannies that you have to get in order to brush your teeth correctly."
The American Dental Association has a new recommendation for parents of children 6 and under: after your kids brush their teeth, parents should brush them one more time.
Dr. Tomaselli says, "If the child wouldn't mind it going up to age eight or nine actually would be ideal."
She says that means extra work for parents… work that some say is unnecessary.
"A lot of people give up and just say well they're just baby teeth so we're just not going to worry about it and they're going to get new teeth anyway," she says.
But she says that's wrong for two reasons.
First, baby teeth serve as a guide for adult teeth, so if there's decay, and a tooth has to be pulled… the adult tooth may not come in correctly.
She also says "If you believe this is your baby tooth your permanent tooth will be sitting right above it. If you neglect this tooth enough where an infection builds up inside the tooth, and migrates through the canal into your permanent tooth, actually you can damage the enamel on the permanent tooth."
So Leanna brushes once… and then her dad brushes to make sure her teeth are clean.
Greg Holden, Leanna's dad says, "Unfortunately I learned it the hard way. I have lot's of fillings in my history and I'm paying the price for it now and you just try to do the best for your kids and hope that they don't have to pay that price."
Experts say kids should use a soft toothbrush and it should be replaced every three months.