The last party we had was for my 1yr old. Instead of having party games, I set up a craft table. I bought wooden pegs ($2 shops, coles, woolies) & then coloured paddle pop sticks, also some old fashion "dolly" pegs, pipe cleaners & some scraps of fabric & the idea was the kids could make airplanes with the pegs & paddle pop sticks & people with the dolly pegs. It would depend on how sensible the group of kids is as to whether you would need to supervise or not.
Play dough is a good idea to have set out also. Glow sticks would provide lots of fun for when it gets dark. ummm Colour pencils & paper. You could print off a heap of pictures off the net for them to colour in. Or I htink toys r us sell big colouring in pads with the Disney princess, cars, toy story etc.
But I think keep it basic & just let them play. Chances are most guests will come prepared with things to keep them happy.