Sugar and bacteria.

For dental cavities to develop there must be three essential factors: bacteria, sugar and time. Bacteria present in the oral cavity “feed” on sugar found in the foods we eat. Caries-causing bacteria digest sugar, producing acids by a metabolic process. The acids then dissolve the enamel.
 
To reduce the risk of dental caries, you should cut down on sweet and sticky foods and brush your teeth regularly. The rule is simple: if there is no sugar for the bacteria to feed on, the teeth will stay healthy. Sugar, on the other hand, is just perfect for bacterial growth.

Sources of sugar.

Remember that it is not only sweet-tasting food products that contain sugar. Crisps and salt sticks also cause tooth decay mainly because they stick to the teeth for a prolonged period, giving the bacteria plenty of time to break complex sugars into simple sugars, and then into acids. It is also recommended to reduce the consumption of sweet beverages, especially before bedtime and at night.

Pay attention to what your child eats and drinks before going to sleep and during the night.
Teach your child how to brush their teeth properly.