It is very difficult for my wee man to pass a stone without picking it up. The purpose then is to find a collection of water even as small as a puddle to throw it in to. This can at times be difficult if the water feature is far away such as when we have just left our house and are walking to the park. As he gets older he gets more ambitious and the bigger the stone the better. It can distract him for hours. He literally can find spot where he just plonks himself down and throws stone after stone. It is really one of the times when he is at his happiest.