We just celebrated our 4-year-old daughter's birthday with a Barbie Princess Theme.  We sent out purchased invitations to the children addressing them to the child as a Prince or Princess as appropriate. When the children arrived, they picked out a royal attire which was made from leftover fabrics such as velvet, velour, lace, netting, and other fancy fabrics and ribbons. The boys had robes and the girls had skirts and dresses with capes.  We took the hats that came with the Barbie Princess themed supplies and added a 24" long toule to the top for the girls. We made crowns out of posterboard and spray painted them for the boys.  The highlight of the party was the castle we made out of PVC pipe and fabric panels all around. It was approximately 10 feet long by 6 feet wide with varying heights.  It's a little hard to explain but we made the front (long side) with a 12" square by 6 foot high tower on each end and a doorway in the middle. On the back there was a 3 foot square by 6 foot high tower on one end and the children could play inside it after they entered the "front door" of the castle. On one of the short ends, there was a room which could be entered from the outside and was 4 feet high and ran the length of the side.  The other short end was just a plain castle wall so they could look out.  There was no "roof" because it would have been too dark.  We made felt flags attached to dowel rods to go on one corner of each of the 12" square towers and 4 flags to go on each corner of the 3 foot square tower.  They were taped on. The curtains were sewn (over 20 yds. of fabric!) with a pocket in the top and elastic loops to hold them to the bottom pipes.  The children loved this so much that no other games enticed them.  We had planned on using the paper butterfly and straw game from this site along with letting them decorate their own little cake.  Decorations were pretty simple because the castle was center stage. We simply put purple cloths on the tables with a themed cloth on the food table. Helium-filled Balloons were tied to the children's chairs which I removed and tied to their goodie bags as they were leaving. We served a cake made to look like a castle with three 8-inch square cakes stacked and two 4-inch cakes (cut from a larger one) centered on top of them. We used sugar cones that were iced and pink sugar sprinkles to make the turrets on the corners of the large cakes with paper flags glued to toothpicks for the flags in top of the cones. We purchased a Barbie edible decal to go where the castle door would have been and used pink and white sprinkles of heart and flower shapes to decorate all of the edges and where the cakes met.  She helped me put them on which made it special for her. Along with the cake, we served veggies with dip, her favorite Chex Mix, frothy punch which used ice cream (the kids didn't even miss not having ice cream then), cheese cubes, and pickles.  To open presents we made a circle with a chair for each child leaving room for me to stand beside the birthday girl. The children then got the present they brought and put it inside the circle. As my daughter opened a present, we passed it around the circle and when it got to the end, my sister layed them out for everyone to see. This really kept the children occupied (and seated!) and prevented them from helping to open the presents as children this age like to do!  Thanks for the inspiration from this site.  There are some terrific ideas here!