Dental Sealants..

Dental sealants are a plastic resin that a dentist bonds into the grooves of the chewing surface of a tooth as a means of helping to prevent the formation of tooth decay.
Sealants are normally placed on children once they are at an age they can cooperate with the dentist. So it may vary from child to child on what age is best to get them.
They are normally placed on the back teeth as it is harder to clean them. A sealant however, can be put on any tooth with deep grooves to help prevent decay.
To read more on sealants you can view this article here.