The last decade has brought about tremendous changes in our thinking about the relation of diet to dental health. All these years it was assumed that sugar was the culprit causing tooth decay, and patients were advised by dentists to avoid sweets, especially sticky ones like chocolates.
The current concept of diet in relation to tooth decay has undergone a tremendous change, and if you have not been in touch, you are in for a big surprise!
Good nutrition certainly contributes to overall good health, but cannot ensure that your children will develop strong, disease-resistant teeth. Other factors are equally important in preventing tooth decay. Many factors influence whether your children will develop cavities, and diet does not matter too much if you pay attention to important steps, such as practicing good oral hygiene, getting enough fluoride daily, going for regular dental check-ups, and having your dentist apply a protective sealant to your back teeth.

Many of the foods we eat, including some of the most valuable foods from the standpoint of human nutrition, provide nourishment for the bacteria in the mouth. These bacteria act on the sugar in the diet and secrete acids, that can erode enamel, and lead to cavities. We feed the bacteria in our mouth everytime we eat carbohydrates.

These come in two types:
Sugars
Cooked starch - like bread and biscuits, which are broken down to sugars by an enzyme in the saliva. The bacteria in the mouth then treat them as though you had eaten plain sugar. Sweets like cake and candy are not much worse for your teeth than bread, biscuits, potato chips, fruit salad, and a glass of milk.

To the bacteria in your mouth, sugar is sugar, no matter what package it comes in. So candy is as bad as, or as good as, apples for the teeth.
Recent research shows that some candy is potentially less destructive to the teeth than bread, biscuits and some fruits (apples, bananas) which were previously considered safe or even protective against cavities, may actually promote tooth decay.

Two important factors affecting tooth decay are:
How often you eat: The mouth normally contains a wide variety of bacteria. These bacteria take advantage of food whenever it is available. So they become active whether you eat a full meal or just a small snack, and they remain active - producing acids that can cause cavities - for about 30 minutes after you eat. This is how frequent eating contributes to tooth decay, and can be easily modified by exerting a bit of self-control.
How long a particular food stays in the mouth after you eat it: The most commonly thought of sticky foods are chocolates. The chocolate is mostly sugar that dissolves in saliva and is cleared from the mouth fairly quickly. However, foods like biscuits and potato chips stay longer in the mouth than chocolates. This is because these do not dissolve in saliva and clear the mouth until they have been broken down into simpler sugars by the enzymes in the saliva. This process is likely to take hours, and in the meantime, the bacteria have a feast and secrete acids, which destroy the enamel of your teeth.