Partially fill each balloon with water and then add air. Place these balloons into the pool and watch them float partially submerged on the water surface. The water in the balloons keeps them from blowing away and makes it fun for the kids to throw them. If they are completely filled with water, they will sink to the bottom of the pool. The look on their faces when they see the pool filled with balloons is priceless.
Every party needs some music to fill the air.
As you are having an outside party, remember to be courteous of your neighbors. Play music that is geared to the age group of children you have attending your party. Make sure your system is in an area where the children will not go and where it will be free from water. Every party needs a couple of structured activities to keep the children amused. Before the party begins, fill water bomb balloons with water and knot them.