For my daughter’s birthday, she received a kit of glow-in-the-dark chalk. It was super easy to make. All you had to do was shake the glow powder and chalk powder in a small container, add a small amount of water, and pour it into a mold. The box said that the chalk would harden in half an hour, but it was not hard whatsoever within that time frame. It was more like an hour, and even then, the chalk was sort of soft and had to be handled carefully to not crumble in your hands.
But it worked. The chalk (especially the yellow and green) glowed in the dark as my children drew pictures all over the driveway one night. It was super fun. The red and blue glowed a little bit, not nearly as much as the yellow and green. This is definitely an activity worth doing with your children, since my kids kept squealing with joy as we were adding more and more details to our glow-in-the-dark chalk masterpieces.