Party game: Get an industrial sized vat of mayo and hide trinkets in it. Kids get to stick their hand in and pull prize out.

Probably only like $35 bucks.

Decor

Mayo labels. Could easily modify a Hellman's label to say Happy Birthday.

Activities

Friendship bracelets made by upcycling mayo packets

Make your own mayo bar, each kid gets an egg. Then just set up different acids on the table (vinegar, lemon juice, pickle juice, etc). Kids throw all that in a jar and then parent immersion blends the jar. Kids can also decorate a label and slap that shit on

Food

Mayo bases dips

Mayo fountain with sliders, fries, and other things that mayo tastes good on

Goody bags

Mayo packets. The MYOM from the MYOM bar.

I'm sorry, what the fuck is the challenge in this birthday party? Is mom fucking allergic to mayo?