I think so. Maybe you could even play with them and they will like you more for it. Then after an hour be like: "damn, too much time sitting for me!" Idea being that it models the behavior. That would be kinda my style. Maybe also depends on their age.

Trying to think back about my school years, the coolest teachers were those who let us play and they were a respectable person. They could even be strict, but reasonable. The worst were those with a witch personality.

Admitedly, I do not have much experience with children, so you should not probably listen to me.