tikilove81 - i would have to disagree with you a bit. I think that playclothes are not appropriate attire for the dining room during dinner.
I agree that dresses for the little ones should be saved for formal nights.
Cute capris with a cute top, a cute little denim skirt with a cute top or a pair of casual pants with a polo or a nice jersey would be perfect for the girls on casual nights. If you have boys, dress them in a pair of cargo pants, khakis or navy blue dockers type pants with a polo or a nice jersey.
Track suits are not appropriate dinner attire for the dining room.