For my son's 8th birthday we had a "Water Squirter Party" in mid-September - lucky for us it was a warm sunny day. We sent out an invitation that we made on a standard size piece of paper with a giant clip-art splash on our computer. To begin the party we had each child follow a string with their name at the beginning that was wound around the jungle gym, trees, and bushes in the yard. At the end of each string was a paper bag with a super soaker water gun in it, which the kids used for the party games and then took home as a party favor. We then began the games in the yard with a large cooler and bucket full of water so that the kids could quickly submurge their soaker to refill them when needed. We split the kids into teams (we had a total of 15 kids) taking turns filling up pails with water (they had to stand behind a line and each got to empty their squirters before their turn was over).  We had a rubber duck in the pail that they had to shoot out of the bucket before the game was finished. We then had the kids try to put out "trick candles" that we had taped to the top of wooden dowels and spread accross the edge of the yard (in a row with at least 3 feet between candles), the kids had to stand behind a line and keep squirting them to get the candles to stay out.  Next, we had the kids try to knock little plastic army men off the tip rail of the swing set in teams, again they had to stand behind a line.  Next, my husband and I sat of the swings and had the kids take turns trying to knock a cup off our heads, again they had to stand behind a line (obviously we got very wet!). We then had a cake and ice cream, and finally a piniata. The piniata was a brown grocery bag that we had filled with individual zip loc bags (one for each child).  The kids had to squirt the bag until it got so wet that the bag ripped and the candy fell out. Fortunately we tried this in advance and figured out that we had to put a brick in the bag to make enough weight for it to break (you'd be surprised how strong those bags are!). Kids who came to the party were from 5-10 years old and all said they had a great time.