How do you dress young kids for spring-like conditions?

We have a trip planned to PCMR next week. Highs are forecasted to be in the upper 40s the entire week. This will be my 3rd time for my twin 9 year olds skiing.

My questions is... how do you dress young kids(9 year olds in this case) who don't live out west for conditions like that?

I've been skiing for 30 +years and know how to layer, but I also have a backpack with me so I can take things on and off. But my kids can't do that while they are in ski school. They've only been in typical winter conditions that require a base layer, light mid layer, and insulated jacket, insulated pants, and balaclava. I'm afraid that they'll be too hot, get sweaty, then get cold... or just be too hot. They're too young to know how to thermo-regulate. I don't want my kids to be those kids that complain to the ski instructor about being uncomfortable. I would hate that for myself, I couldn't imagine having to deal with 6 randos like ski instructors do. I don't mind my kids being uncomfortable at times. IMO it develops resilience, but in those times I'm in control of how much they can take and where their breaking point is. I would hate for them to be too cold or too hot in a situation where they have no control and have no idea how much longer they would have to deal with that. In turn making them hate being in ski school. They are better than average about not being cold, but out on the mountain all day is a different story.