Play games, Eat, or both.
On fun days I like to bring in board games, the Pictionary board is fairly colourful, for example. Since the cards included in the actual games are usually too hard for my kids, I use the cards from the book we are studying, or an easier level and play with those. As long as they are rolling dice and drawing, it doesn't feel like a study session for them.
One
really fun day I bought a huge tub of cheap ice cream and several flavours of soda pop, and made
ice cream floats for everyone. The kids thought I was nuts, they had never seen anyone put those two ingredients together before
.
Have fun with your parties! Let me know what games or activities you come up with.