A backwards party is a lot of fun for little ones. They are just learning about opposites and this really cracks them up. The children should be instructed to wear their clothing backwards in the invitation.
When you open the door, say "Goodbye, go out!" Typical party games like Pin the Tail on the Donkey can be switched to Tape the Trunk on the Elephant with ease.
We went so far as to sit the kids UNDER the table and gave them the icing to eat in little dishes, then the cake- and that really cracked them up.
They thought they were really getting away with something wild, when in reality they probably had less icing this way!
We sang Merry Christmas to Me instead of Happy Birthday to You- and the birthday child closed his eyes as he opened the presents and tried to guess what it was (older children would guess wrong- like "A truck" when the gift was clearly a book, etc.).
After the cake, we served pancakes for lunch, and put the syrup under the pancakes - this can just take so many avenues of silly- and the sillier the better.
The kids loved playing musical chairs without chairs or music - yes, it can be done by simply turning the television on and off and have the kids drop onto taped X's on the floor.
The host has to just play up the SILLY aspect of the whole thing, and the "cool" children may just be too cool for such nonsense, so be aware of who is on your guest list!
When the party was over, we told them all "You're Welcome for Going- Hello!" Every child walked backwards from the front door giggling and telling their parents all about it.