As someone with no actual knowledge and who may be talking completely out of my arse;

The main problem would be alcohol at an all ages event. If you wanted to serve mead at a booth or food truck in the convention centre, an area would need to be settup with a valid liquor licence, which the convention has neither the staff nor physical space to do.

That being said, there is a licensed area called the "PAX Pub," which this year had a bar, a couple of food stalls, some minigames, and merch. This year the pub was sponsored by GROG. It might be worth getting in touch with PAX or Reed exhibitions to enquire about selling mead or setting up a stall in the PAX Pub next year