I think you could have a "Tinker Table". It would be a place where the kids could "tinker" just like in the movie. You can just put a bunch of tinker toys for the kids to play with, but not necessarily take home. The playdough and craft ideas people have would also work with a "tinkering" theme. There are many ideas that you could put there that would work.
I also liked the idea someone had with "pixie dust". My DD's preschool has taken sugar and added food coloring to it. They made many different colors and put them in squeeze bottles (those generic clear ones for ketchup/ mustard/etc you can buy at Smart & Final). Then the kids created designs as best as 3 & 4 year olds can do in very small clear cups with lids.
The only thing is they used liquid food coloring and some of the sugar clumped. I don't if it would've worked better to prepare it several days ahead of time and really work to ensure it doesn't clump. Or, I might recommend finding powder food coloring, but I think you might have to order that online. Either way, it's a favorite with the kids!
Sounds like your DD will have a fabulous birthday. Great job mom! Have fun!