Before age 6, kids need your direct supervision when they brush and floss, since they lack the motor skills to do them right, says the American Dental Association (ADA). Before the first baby tooth arrives, at around 6 months, you can wipe gums daily with a clean, damp cloth. But once her pearly whites start to appear—she may have all 20 by her second birthday—brush 'em.
6 months to 2 years
Hold a soft, child-size toothbrush at a 45-degree angle; go over eating surfaces and the inside and outside of teeth in a circular motion, half on the gums, half on the teeth. Skip fluoridated paste for now; swallowing too much fluoride can discolor permanent teeth. Use plain water or a fluoride-free toothpaste, such as Orajel Toddler Training Toothpaste. If your water isn't fluoridated, ask your dentist about a supplement.
2 to 4 years
Continue to use water or fluoride-free paste until your child can spit into the sink. Then you can use a small amount of fluoridated toothpaste. Around age 4, when back molars are touching, start to floss. Wrap it in a "C" shape around each tooth and glide it gently.
4 and up
Let your child brush by herself with a soft brush, but follow up. Teach by letting her mimic you. An electric brush, such as the Crest SpinBrush, can help kids brush more easily and give them more gum stimulation. Whether she's using a manual or electric brush, she'll be ready to brush solo about the time she can tie her shoes.