You will be amazed how quickly your kids pick it up - especially your older two. By the end of our first PC trip (when my older two were 5 and 7) they were both very comfortable on the greens. Now we ski groomed blacks and all blues with them. They kick our butts through the moguls. My little one still is a green hill skier - an easy groomed blue that is nice and wide is fine but otherwise he gets out of control.

We usually put our kids in all-day ski school for the first few days and then pull them out starting with the oldest and working our way down so by the end of the trip we are all skiing together. But we always ski with the older ones (now both of them come out together to ski with us since both are advanced intermediate/advanced) for a few days but really I am done with a day or day and a half of skiing with my youngest. When he was 4 I often pulled him out after the pm hot cocoa break and skied the end of the day with him. Last year we pulled him out for a day and a half at the end which was fun, but it definitely cramped the style of the older two so it was fun to have them out on their own so the four of us could cover more terrain.

Depending where you ski, group lessons can be very small. At Deer Valley - my four year old was either out one on one or with two kids. Last year when he was five he was in a group of three or four, tops. The older kids were in a group of five or six, but of course they are much more accomplished skiers and they were with friends so they wanted to have a group. We had five 9-10 year old girls ski together all week and at the end the instructor said next time we should definitely just get them a private instructor (one day they had a random kid in their group that really slowed everyone down) so this year we will have 3 girls (10-12) together and will probably go that route for 3 days and then they will just ski with us. But even with five kids, the rates were slightly higher for private vs. the group ski school rate - I guess my point is don't stress about the quality of group lessons if semi-private will break the budget. They will still learn very quickly.