great summer idea-ice eggs - Freeze balloons filled with water and small toys. Cut balloon off and play with eggs outside. Provide spoons for cracking ice and digging treasures out. - looks like a great activity for hot summer days!
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.
This would be a great experiment for elementary school students. Apple rotting experiment - check out this apple science activity and see what happens to apples left in air, water, vinegar, and oil for a w.