This Water Slide Birthday Cake was made for my daughter's 6th birthday party held at a water park. The bottom cake was a single 12x18 layer, then a 2 layer 8" cake & a 2 layer 6" cake. The slides were made by molding Wilton ready-to-use Gum Paste then painting with a Wilton gel icing color diluted in vodka.
The water coming down the slides is pearl colored Wilton Sparkle Gel. I used an Ariel playset slide as the mold for the pink slide and the yellow slide mold was a spiral slide originally intended for use in a hamster cage. The kids are made out of Wilton Ready-to-use Rolled Fondant (just like playing with play-doh). The supports under the slides were two turrets I had from a castle kit I had used 2 years ago.
The pink slide was partially under the 6" layer cakes to provide natural support. The yellow spiral slide had a hole cut in the bottom and lollipop sticks inserted in the hole and into the cake sticking up about 1/2" to keep it in place. I then covered the protruding sticks with the sparkle gel to make it look like the water source for the slide and put a fondant person directly in front of it to hide them (guess I could have stuck the fondant person on the sticks to cover them, but it was fine the other way).
I also used buttercream icing the color of the slides and polka dots to add additional support to the slides where ever they touched or almost touched the cake. This was really fun to make. It was my first time using fondant and the second time experimenting with gum paste, both were very easy to use (my 6 year old daughter helped with the fondant people).