As your child gets older, use a soft bristled tooth brush to clean her teeth a couple of times a day. Fluoride can be toxic and cause spots on teeth in large amounts, so use a tooth paste that is safe for children, and help your child learn not to swallow the tooth paste. Until your child is about 3 years old she needs help to clean her teeth well, and then you should still keep an eye on her tooth brushing, to make sure she's getting those teeth nice and clean! You can try letting your child brush all by herself in the morning, and then have mom or dad do it before bed. If your child tends to focus on the front teeth and misses all the rest, you can try playing "find the hidden teeth!" to get her to clean all her teeth. You can use "disclosing tablets", which, when chewed show color on any plaque that is left behind after brushing. This can be a fun way to help your child understand why she needs to brush and get everywhere!
As soon as your child's teeth begin to touch, it's time to start flossing! Using plastic flossing tools can be very helpful when flossing with a little one.
No matter what, you may run into resistance when it comes to teeth brushing, but starting at a young age can help a lot! Let your child watch you, your partner, or an older child brushing teeth even before baby has teeth. Babies are very interested in everything you do, so let them see you modelling the behaviors you want them to have!
Info taken from: http://www.webmd.com/oral-health/tc/basic-dental-care-infants-and-children