Make a CLOUD! Fun science activity for kids. For younger children, this will have to be a demo (aerosol hairspray or blown out lit match is needed in a glass jar), but the children can still observe and record their Scientific method steps
Use chemistry to make a bouncing polymer ball, then alter the procedure to see the effect the changes have on the characteristics of the bouncing ball.: Make a Bouncing Polymer Ball - Introduction and Materials
How to Make a Catapult for Kids - this fun STEM Activity will keep them busy for hours! Four to six Popsicle sticks, three or more rubbed bands, glue (or glue gun), small cap, cotton balls or other small items (buttons?) for catapulting.