I've set aside time for science, officially, once a week, on Tuesday afternoons. Sometimes, we'll just be reading a science book or baking (because that's always scientific, don't you think?), but I did purchase Bubbles, Rainbows and Worms for some fun ideas.
One recent afternoon, we experimented with mixing colors. First Son has been particularly interested in mixing when painting, so this was a natural addition.
First Daughter pretty much just made a mess, and tired of it pretty quickly. I wish I had thought ahead more and read Mouse Paint earlier in the day. (We have it. I just didn't think about it.)
I don't intend to be systematic with science, just have some fun. I'm sure it will often be blended with our Nature Study as well.