You made the water bombs and the kids had a great time throwing them at each other and getting really wet in the process, now let's use those same water bombs for sponge paining! I am a HUGE advocate of being able to use things for more than one purpose. And with washable paint you can use these water bombs to make really cool paintings.
Pour washable paint on paper plates and instruct the kids to tap their sponge into the paint and then create a cool pattern on the paper. My yoga kids loved combining the colors and shapes on the page. Then when they were finished creating art with the sponge they decided to make some foot art and used the sponges to put paint on their feet and then step on the paper.
Try using the water bombs with painting outside and see what art your kids create.