Starting from a very young age, kids develop a strong attachment to their parents. Part of this is easily explained by the fact that parents are typically the ones caring for and protecting the child, but the reasons go much deep than that. Children learn to adopt personality traits from their parents. On a deeper level, a lot of what children see in their parents is actually themselves and what they aspire to be.
There are many different levels to the bonds between parent and child, but this is part of the reason that the relationship is so sacred to us. As much as our parents love us, just like with this boy, we want them to know that we love them too.