M.R.
Lactose is the milk sugar and the casein is the milk protein. It's more likely he has a problem with the casein than the sugar, in which case, the Lact-Aid would not work.
I also don't think that the lactose pills help your body any- though I could be wrong- but more help disguise the symptoms so you are not in pain. I would do a lot of research before I tried it, especially with one so young.
Why do you feel your 7 yr old is cheated? If you don't go to those places, how will she even know what she is missing? I have a 10 yr old and a 3 yr old, both with different dietary issues, and we manage to avoid eating out unless it is a place that is safe for both of them (which is a really rare restaurant- mind you!)
At home, we all observe everyone's intolerances so there are no issues. Yep, even the adults, and even after the children are in bed. If avoiding dairy makes the child better, then chances are one or both of the parents has the issue too, so we avoid the same things as our kids and it does make a difference in how we feel and how we interact since we are all on the same "team" with what we eat.
I have a food blog, if you are interested- coconut milk ice-cream is really easy to make, as are popsicles. We avoid gluten, pasteurized-dairy, sugar, and a whole host of other things and even my 10 yr old doesn't feel like she is "missing out."
I hope this helps rather than sounding judgmental, which is not at all how I meant.
Hugs,
M.