Children's parties and food allergies

http://www.kidsbirthdaypartieslongisland.net/

Sooo the invites to the party of the year (well hardly) went out on Monday and today we had the first reply. Together with a request from the mother about the food that is bring served; her son has a dairy allergy. She would like to know what we are serving so she can recreate it in a similar manner so her son won't feel left out. All very admirable and committed, which I'm sure you have to be when dealing with food allergies, however we intend to serve the supermarkets best bargains! Value sausage rolls, pizza slices, jam sandwiches on basics bread, cheesy puff balls, etc.

So what do we do? Do I text the mum in advance with a list of all the foods so she can sort it out? We weren't intending to buy the stuff until the day before, or maybe even the day as there's very little prep. Or are we supposed to serve dairy free food to all the kids (surely more expensive) so this boy won't feel left out? Risk him feeling left out and serve him special food?

I hasten to add the mum was lovely about it and her son is a nice little chap. She said that often people don't invite him because it's difficult to feed him, poor lad.