Stay at the playground. Play with sand and water. Find seeds. Sit in the shade, and in the sun. Set ice in the shade and in the sun. Write with ice on a sunny sidewalk. If there's a brass plaque at the park you can set a piece of ice on it when it's hot and get the letters in reverse, melted into the ice. Don't talk about WHY those things happen unless the kids ask. Just let it happen. They'll figure it out.
Once they get the hang of figuring those things out, they'll be able to figure out harder things. If they practice on cheap and easy stuff (ice is great—in the bathtub for floaty-toys, crushed ice for snacks...), they'll be calmly confident about figuring out increasingly harder things.
photo by Nina Haley