A little science...This would fascinate kids. Rainbow roses, you can do this by splitting the stems into strands and placing each one in food colouring the roses draw the liquid colouring into the petals, amazing! And that was my science fair project in middle school! :) I'm not sure if this would work with Roses but maybe carnations or another flower.
Another science fair idea: Make rainbow roses by splitting the stems into strands and placing each one in food coloring. The roses draw the food coloring into the petals. Maybe do this for mothers day from the kids