Here's how to keep cavities away: Start good oral habits early. Teach kids to brush at least twice a day with fluoride toothpaste and to floss regularly. Get enough fluoride. Regular use of fluoride toughens the enamel, making it harder for acid to penetrate. ... Limit or avoid some foods. How do you prevent tooth decay in children? Preventing Tooth Decay in Young Children Teach your child to brush and floss every day. ... Prevent prolonged contact with sugars in formula and breast milk. ... Be smart about juice and sugary drinks. ... Introduce an open cup for beverages other than breast milk or formula at age 6 months. ... Provide your older baby or toddler with healthy foods.