It is how it's meant to be.
The light in an adult mind is meant to be brighter than that of a child. This is why it's commonly said in some places that an elder sees far ahead sitting on a chair what a younger human can't see standing. Well, this is true if the elder keeps the mind pure and not darken with bad information or knowledge. If the child is constantly updating his mind with good and higher knowledge while the elder darkens his, definitely the child will become brighter.