How do I get the kids to throw the ball in and not?

Set up a race. Get the kid who wants to run it to start at a point say 20 metres from the wicket. Stand his mate next to him with another ball. On go, get kid 1 to run and kid 2 to throw it into a wicket-keeper, and see which ball arrives first. When he sees that no matter hard he runs, he will lose to the throw 8 times out of 10 (allowing for wild throws) he might start to think. Then add a running batter into it. He can start from the other end, and all 3 start on go. Do it 10 times and count how many times out by running in, out by throwing in and not out. Should get a clear lesson....