Hi Celiacmom, and welcome!
I'm sure the recent diagnosis of your son's condition is a tough challenge. Teenagers are especially sensitive to anything that makes them seem different than their peers. I hope his friends and school are being supportive. Celiac disease is getting much more attention in the press these days, that should help.
I think having him avoid dairy for a while is probably a good idea, many people do develop lactose intolerance shortly after they go GF, it happened to my daughter.
You might consider some soy based substitutes for the milk and ice cream he is giving up. Be aware that some types of soy milk do contain small amount of gluten from barley malt or other sources. I buy Trader Joes brand and WestSoy brand soy milk products. I prefer the WestSoy unsweetened soy milk, it seems to me to be much like I remember cows milk, without as much of the beany taste you get from some brands. The ingredients list for the WestSoy soy milk (unsweetened variety) is: filtered water, whole organic soybeans. So it is clearly GF! There is also Silk brand soy milk products, often in the dairy case in supermarkets, they make a great chocolate soy milk.
There are also several brands of soy-based "ice cream" that we buy sometimes. I prefer the Soy Delicious brand. I see it at health food stores, Trader Joes, and even in larger supermarkets like Ralphs (here in California).
Please feel free to ask any questions, voice any concerns, or ask for any help you might need. We try to be friendly around here.
Steve