Some cool ideas that came up for programs for younger kids:
Changing it up, taking the train set away for the summer, replacing with scientist dress-up station, with lab coats, goggles, beakers, lab supplies for creative play and exploration
Creating a hydroponic garden or any kind of garden with kids for summer experimentation and overall deliciousness
Gross stuff programs, including suggestions for making homemade edible earwax, poop cookies and more.
Fossil making (here's one method)
Borrow the Star Lab from your area CESA for a program