I shop at Publix every week, multiple days a week in fact (Have you seen the price of groceries lately?), so therefore I know that Publix carries cupcakes, little ones, individually wrapped ones, themed ones, Holiday ones, etc.. However I don't have a clue what certain grocery stores carry in New England, since I'm not from there. So if I needed cupcakes in New England, I'd have to ask, as we all know it's better to ask then to assume!
I know for a fact that you will find what you need and want at Publix and better yet they will be happy to make what you want, given 24 hours notice. Wishing your children, Magical Disney Birthdays w/ or w/out cupcakes! Have a wonderful vacation!
P.S. Shopping at Publix for 30 years and never ever thought to try the canolies, imagine that!