How to keep a child busy for hours in the summer: DIY: Giant Ice Cube Awesomeness - filled with plastic animals, dinos, and such. And I'm sure you could put in food dye before its frozen to color it like the ice block in the photo.
Sensory / Pretend Play Invitation to Play: Ocean sensory play with gelatin - oh, so messy but delightful! Use plain gelatin with a small amount of food coloring instead of the heavily colored blue jello packets.
Play Create Explore: Baby Oil Sensory Bags = baby oil, food colouring, a little bit of water, glitter, objects to find (smooth). Put in ziplock bag and duct tape for leaks and little fingers who would like to open it.
DIY: How to make a cloud! Wish I had know this when Nadja asked for a cloud for Xmas, we only came up with a dry ice version. She still has a jar of "condensed" cloud though. The cloud can be suspended from ceiling with light behind