I am the OP of the other dairy allergy thread. Sorry for not following up there; I was busy with work, even in the evening.
A few years ago, I discovered that I have a dairy allergy, which I believe I've had since childhood. Looking back, there were signs like when I ate a gyro and threw up on the street after just one bite—eating tomatoes with feta cheese and coughing like nuts. I also have issues with raw onions, pepper, and celery, so I initially thought those were the main culprits.
It is a difficult allergy to deal with. I am from Europe and love sour cream, cheese, butter, and ice cream.
I am lucky that I cook my own food all the time, and I am a good cook. I eat a lot of veggies-based dishes, with a bit of meat.
I used to eat spinach with sour cream, but not anymore.
Almond milk is not to my taste, so if I am making chicken cutlets, I mix eggs with cashew milk for dipping in the egg and flour part of the process. Daiya is not good at all, in my opinion.
But there was another brand at Wegmans recently, which is okay. I bought their vegan feta, and it tasted okay with my tomatoes. It is not feta—it will never be feta—but it was adequate. Maybe it is Myokos or Violife.
Cashew milk is also good for cakes and such; all others are too liquid. Some margarine (be careful, many margarines actually have dairy in them!), or I can't believe it's not butter, is also good for baking. Heck, you can go one better and buy leaf lard if that is something you are okay with. Some pudding mixes do not have dairy powder in them!
For pasta, vegan feta and their other brands are okay, too. However, to achieve a similar flavor, you will have to put much more vegan cheese in than you would regular cheese.
Other than that, I just cook without dairy.
Look up Lenten cookies and desserts. Many cultures observe Easter Lent, meaning no animal products in food. Sure, you can see to modify them to include eggs.
I order pizza without cheese, though. The vegan cheese they offer is not good, in my opinion, and I find it great without cheese at all. You can choose regular meat lovers or whatever your child likes, but no cheese. It is easy to do so today when you can order online.
Thai restaurants instead of Indian. Always, always in a Mexican restaurant he needs to order no cheese or sour cream. As I am such a food snowflake, no cilantro for me either.
(Honestly, I love almost all food, but these few are a major issue for me; raw onion, celery, and peppers will make me sick immediately.)
As shown in my thread, I am still struggling with eating out and being firm about my allergy. I hate being the "fussy" person and having so many issues with food, so I just don't voice it. But with the advice I received here, I will try to be more assertive. Hey, it is a dairy allergy; I will not just end up having some lactose issue; it is not the same bloody thing!
And chocolate! Why, why me? Nothing beats Milka or other European chocolate, but some cooking chocolates are not as bitter, and most will not have dairy.
But there might be butter even in Chipotle rice! There are different reports about what goes in it. There is butter in the nan bread dough, milk in donuts, bread rolls, and most pastries. But not in all pastries; cheap margarine-filled deserts are now my friend!
Also, steak in restaurants is cooked in butter! Jacket potatoes are drenched in butter. Many deli meats and sausages contain dairy. Fish sticks often have dairy! It is endless.
Honestly, it is best to cook at home. Make sure he always has allergy meds with him. I presume he will not die from it as it was just diagnosed, and he ate a lot of dairy until now. But it is causing the slow killing of his immune system; at least, that is what I was told. If I have a donut now, I will start coughing and choking. Reaction is immediate after not eating dairy for a long while.
https://www.tasteofhome.com/collection/foods-that-contain-dairy/
Good luck, OP; it is not an easy road ahead. Please don't get mad at him when he eats dairy, such as in a pastry, or has chocolate; it is really hard to avoid.
And now, the end, sorry about this War and Peace Treaty on dairy.