Hi,
Bethany response is right on the money. From experience the puppet shows and magician shows do not hold the kids interest. The dressed up cartoon figures scare some of the kids and it is boring. They love the bouncey things, bubbles galore have more than one station.
Perhaps hire or ask a teen relative to be the leader and play some games: duck duck goose or make an easy obstacle course with a ball. Water balloons are also fun if you do not mind getting wet and cleaning up the bits of balloon everywhere. The children need an upbeat organizer for the games and keep the energy high. I am curious if the treasure hunt will work for 3 yr olds, but it is a great idea. I went to a party that had a cotton candy maker and an old fashion popcorn machine. Lots and lots of balloons, kids love the balloons and bubbles it really makes the party fun.
As for the adults, they will enjoy watching the kids, knowing they are involved and having fun. Some will partake in the cotton candy and popcorn and perhaps a water balloon or two.
Hope this was helpful. Have a great party.
D.