Home improvement stores sell component based sprinkler systems. You buy some hose, connectors and valves. Choose some cool sprinkler heads. Then hook the whole thing up to your hose.
In our case, my husband installed a splitter down on the hose faucet so he'll still be able to hook up a regular garden hose and then ran the sprinkler system hose up to the deck level. He attached the hose under the deck rail. I just made that sound simple, but it did take him several hours. Then he pierced holes (with a special tool) in the hose and installed a smaller hose with a valve and sprinkler head every few feet along the deck. With the valves, the children can turn each sprinkler head on and off individually. We also left two of the smaller hoses free flowing and called them kid faucets. They can open the valves and use them to fill cups, make "water snakes", spray each other (neck down), or anything else that suits their imagination. There is also a master valve they can use to turn the entire thing on and off at will.
Hopefully the pictures will give you an idea. We got it up and running today. The children had so much fun. I intend to send the children out to play every day this summer in the morning when the deck is in the shade. I'll simply send them out in clothes that I don't mind getting wet. They will be able to play in the sprinklers whenever they like, and use the "kid faucets" whenever they like as well.