It has to be remembered that the children do not have the same stamina that the adults have when it comes to skiing. For every little ski maneuver the kids perform it absorbs a great deal of their energy. If they are not used to this type of exercise then they will tire quickly. For those of us with kids we all know how difficult it is to reason with a tired child who often turns into a tyrant.
You can prevent some of this burn out by conditioning the kids to being outdoors at the beginning of the cold season. Small daily outing of playing outdoors will condition them to the cold weather. This means they will adapt and endure it for a longer period of time when you are away on your ski trip.
Make sure that the kids get to bed early consistently before the ski trip. If they are up too many late nights they are going to be drained before you even arrive at your ski destination
These are just a few helpful hints to help make your next ski excursion a little more pleasant if this is going to be a family event.