Take the following steps to prevent tooth decay:

• Take good care of your own oral health even before your baby is born. It is important and OK to see a dentist for oral care while you are pregnant.
• Whether you choose to breastfeed or bottle-feed, it is important to take good care of your baby’s teeth.
  • Birth to 12 months: Keep your baby’s mouth clean by gently wiping the gums with a clean baby washcloth. Once you see the first teeth, gently brush using a soft baby toothbrush and a smear (grain of rice) of fluoride toothpaste.
  • 12 to 36 months: Brush your child’s teeth 2 times per day for 2 minutes. Use a smear of fluoride toothpaste until your child’s third birthday. The best times to brush are after breakfast and before bed.
• Never put your child to bed with a bottle or food. This not only exposes your child’s teeth to sugars but can also put your child at risk for ear infections and choking.
• Do not use a bottle or sippy cup as a pacifier or let your child walk around with or drink from one for long periods. If your child wants to have the bottle or sippy cup in between meals, fill it with only water.
• Check to see if your water is fluoridated. Your child will benefit from drinking water with fluoride in it. If your tap water comes from a well or another non-fluoridated source, your child’s doctor or dentist may want to have a water sample tested for natural fluoride content. If your tap water does not have enough fluoride, your child’s doctor or dentist may prescribe a fluoride supplement. He or she may also apply fluoride varnish to your child’s teeth to protect them from decay.
• Teach your child to drink from a regular cup as soon as possible, preferably by 12 to 15 months of age. Drinking from a cup is less likely to cause liquid to collect around the teeth. Also, a cup cannot be taken to bed.
• If your child must have a bottle or sippy cup for long periods, fill it with water only. During car rides, offer only water if your child is thirsty.
• Limit the amount of sweet or sticky foods your child eats, such as candy, gummies, cookies, Fruit Roll-Ups, or cookies. Sugar is in foods like crackers and chips too. These foods are especially bad if your child snacks on them a lot. They should be eaten only at mealtime. Teach your child to use his tongue to clean food immediately off the teeth.
• Serve juice only during meals or not at all. The AAP does not recommend juice for babies younger than 6 months. If juice is given to babies between 6 to 12 months, it should be limited to 4 ounces per day and should be diluted with water (half water, half juice). For children 1 to 6 years, any juice served should be limited to 4 to 6 ounces per day.
• Make an appointment to have your child see the dentist before the age of 1. If you have concerns, the dentist can see your child sooner. Find a pediatric dentist in your area on the American Academy of Pediatric Dentistry Web site or insurekidsnow.gov​. If no dentist is available to see your child by age 1, your pediatrician can look inside of your child’s mouth, apply fluoride varnish, and talk with you about how to keep her healthy.

The AAP recommends that:

• All infants receive oral health risk assessments during well-child visits starting at 6 months of age and periodic fluoride varnish application from the time the first tooth erupts through 5 years of age.
• All children should be referred to a dentist as early as 6 months of age to establish a dental home. If a dentist is not available, talk with your pediatrician about how to maintain your child’s oral health and find a dental home.
• All children in their early toddler years should have a thorough initial dental examination and regular dental care whenever possible.
• Parents should limit food and drink exposure over the course of the day to 3 meals and 2 snacks (with healthy food choices and limited juice). More frequent exposure to sugars in foods and drinks makes it more likely that children will develop decay.
• Parents should brush their children’s teeth with fluoride toothpaste as soon as they can see the first tooth coming in (erupting).

Source: https://www.healthychildren.org/English/ages-stages/baby/teething-tooth-care/Pages/How-to-Prevent-Tooth-Decay-in-Your-Baby.aspx