Help! I Need Some Fun Ideas For Things To Do With Kids

Starting tonight, I am watching my friend's children on Monday evenings and I need some help on finding some fun things to do with them.

They have three children, a girl and two boys.  Their youngest is less than a year old and the other two are four and two.  I'm not worried about the baby, that's easy but I'm not sure about the other two.

I got them both coloring books and crayons, which means I get to color tonight but what other fun things can we do?