Sealants are thin plastic coverings that are "painted" on to your child's teeth and then cured. Once this easy, painless procedure is performed, the sealants can be expected to last for about five to six years.
The chewing surfaces of your child's teeth are full of indentations and grooves. While these grooves make it easier for your child to effectively chew food, they do have a tendency to trap food. Since kids aren't quite as coordinated as adults, it can be difficult for them to remove all the traces of food, plaque, and bacteria from these surfaces, making them a prime location for cavities.
The sealants create a barrier between the surface of your child's teeth and the food they are eating, preventing cavities from developing. They are colored to blend in with your child's teeth, and it is highly unlikely that anyone else will be able to see them.