Playing in the sand tray is science! Making piles of sand, seeing how it crumbles with no water and sticks with some water. Making tunnels and roads from sand may seem like fun but it is also science, as is playing with a water tray - or a washing up basin and some pots and pans. Watching frog spawn turn into tadpoles, sowing seeds and watching them sprout and throwing grain, then watching birds come and eat it is also science.
My father showed me that you could strike the old fashioned types of match on a window pane, because there was sufficient friction to heat the constituents to the point where they went on fire. (Probably be a total safety "no-no" these days).
Try lying in the garden watching ants go in and out of their nest, or bumblebees, provided you don't annoy them to the point of stinging. Climbing trees or jumping onto the ground is science - you're learning about gravity (we fall DOWN, not up), you may also learn about cut knees, grazes, getting skin washed to remove dirt and germs and the use of sticky elastoplast for cuts and bandages for sprains.
I sometimes think kids today don't have half the fun or learning opportunities we had as children. I grew up in a coal mining village and we had a lot of freedom, with few cars on the road. We had plenty of time to play, very few toys, so you went outside to play and learned about streams, mud and dirt and animals. There was very little TV available and only 1 hour for children. TV closed down for the night at 8pm.