It is getting nice outside so take your kids for a walk.
Tell them today we are going on a colors walk. They need to find all the colors.
For your toddler just point out colors that you see. It can be very casual. There are green leaves, a red house, blue sky etc. You can try to use the colors of the rainbow a few times through out your walk. Red, Orange, Yellow, Green, Blue, Purple (Yes, I know it is indigo and violet...)
Preschooler: For your preschooler make it a hunt. Start with a color like red and see who can find something red. Then move on to the next color.
You can take your camera along and take pictures to make into a "color book". Just print or develop your pictures and put them into a 99cent photo album.
EXTEND: Did they love it? GREAT! Tomorrow do the same thing but use numbers or letters.