It is perfectly safe for children to take the adults tablets. Depending on your child’s level of lactose intolerance, you may find half to 1 tab of the adult tablet is sufficient to eliminate symptoms. Remember, any excess lactase enzyme is simply eliminated through the digestive system.
The lactase levels in humans naturally decrease when a child is weaned. For most children there is still enough of the enzyme produced to digest the dairy in our diets, but for others they drop too low to be able to breakdown the lactose. This could be temporary, due to a recent bought of gastroenteritis or a course of antibiotics or it could be permanent. Read more about the Risk Factors of Lactose Intolerance here.