wow! wish i could offer you some advice but thankfully there are no food allergies in my family. hopefully other moms will be able to give you advice. i'm sure if you do a google search you can find some recipes that accomodate the allergies & i'm sure there are books you can find on the subject. they have books on just about everything now. good luck!
It's really simple. Stick to whole foods instead of processed foods. If you still want processed foods, look for things that are gluten free. Stores have started getting more on board with gluten free products so they seem to be pretty easy to find. They can get expensive, though. You could check out gluten free recipes and make your own stuff as well.
As far as dairy goes..... No one needs dairy so that isn't an issue. Almond milk is a great alternative to baking and drinking, as is coconut milk.
You could also ask to get a reference to a nutritionist who specializes in food allergies.
there are a lot of gluten free items out there even mc and cheese. takes a little to get use to it but its not bad. I will look up some recepies at work. I ran the dinning department of a retirement facility so we have a ton of recepie. if you want me to e msil you some monday send me an e mail to. firstname.lastname@example.org