Recently, I went to the waterpark with my 9 year old niece. It was lots of fun. One fun thing they had at the waterpark was a giant bucket that filled with water. When it was almost full, it would tip over and drench anyone who stood beneath it. I thought it was the coolest thing and so did all of the kids. Getting 500 gallons of water dumped on you is more fun than it sounds.
For this pumpkin I would employ the same "fill and dump" technology using a fishtank pump. The result would be a baby-faced pumpkin that would periodically spit-up. It will be fun.