Black cardboard cut out frames with some coloured cellophane = fun colour window shapes. I initially made them for Otis but Caspar liked them just as much. I was inspired by Kate's post on window blocks.
pine needle discovery bottles - Make with the kids at preschool. Add water, pine needles, and glitter to a water bottle and hot glue cap on top. Use different evergreen, so the kids can see the difference. Kind of a 'I Spy' theme