- wooden blocks
Before class starts build a fortress out of Legos and one out of wooden blocks.
While talking about making choices now about what you will do when you're tempted you can use the fortress of wood blocks as someone who didn't decide before hand what to do when a temptation came and the lego fortress as someone who decided what to do before they were tempted.
Have a child toss the ball at the wood fortress (remind them to toss softly so as to not break anything in the room). If the ball makes contact a few blocks will fall and it shows the difficulty of defending against temptation. You could even have a child try to build up the fort as the ball heads towards the blocks but even with them moving blocks to build it up. They won't be able to save all of them from falling and possibly knock others over trying to protect it.
Then show them the Lego fortress be sure to build it up strong . I prefer the interlinked double-wall design. the have a child toss a ball at the lego fortress, and as long as they don't throw it like a base ball, it should stand up to it. This can be shown as someone who decided what to do before the temptation arose.
(Jenny - I tried to find pictures of an interlinked double-wall design, but I don't know what it is. If you can share instructions or pictures of how to build a super strong Lego wall, please post below.)