My Sister's Kids (2001)

Erik Lund is a professor in child psychology. When his sister and her husband go on vacation, he is left in charge of their five children. He really feels up to it, since he will now be able to try out his child-psychology skills. But reality is different from theory, and children don't always do as they're supposed to according to his textbooks. These nieces and nephews of his soon fool him into doing as they please. But then they start to realize that if they can make him serve them hot dogs and hamburgers and let them watch as much TV as they like, they can also make him help them restore their old house so they won't need to move, as their parents are considering doing. And since their uncle is nice enough to help them, they decide to find him a wife.