Small foam brush or small paint brush (no paint needed though!)
Small cup of water
Scissors (if old enough otherwise, hands work fine!)
Take tissue paper and either cut into small pieces or if your kids are smaller, they can simply tear the pieces easily. Using the paint brush, dab a small amount of water onto the egg and then stick tissue paper onto the egg. Repeat until the egg is covered with tissue paper - let your kids do them in single color, in a design, or in a random mishmash of colors of their choosing. Let the eggs completely dry.
Now, you can either leave the eggs as is and have them decorated with the tissue paper on, or they can carefully remove the tissue paper, and the tissue paper has dyed the egg beneath in the same design as the tissue paper.