Ohhhh...hit the garage sale & thrift store toy bins and buy a bunch of the small Disney themed toys for favors - bring them home and either run them through the dishwasher or let them soak in some bleach water.
Depending on your budget you could conceivably find some Disney t-shirts at the thrifts for the kiddos to slip on over their party clothes so everyone is dressed Disney as well. Of course, wash them too!
And don't forget to explain to the cashier what you're doing and ask if you can have a small discount.
Sounds like you are a fun auntie!!