How can you get your children to understand how virtually pointless it is to buy lottery tickets? Well, for starters, since many states earmark some lottery proceeds to supplement public school funding, understand that your kids may be hearing their teachers and other school employees extol the virtues of buying lottery tickets "to benefit schools." What a sad state of affairs.
Have your kids imagine looking for someone they know in New York City (or any other very big city they're familiar with). Then have them imagine picking a street in any of the five boroughs completely at random, entering a random building there, and knocking on any door. Do they think it's likely that their friend will answer the door? That's a very rough way to convey how improbable it is that they'll win a typical lottery. They're more likely to be hit by lightning than win big money in a lottery -- not that we're suggesting sitting them outside in a thunderstorm holding a golf club in one hand and a lottery ticket in the other hand to test this theory or anything.
It's also good to explain why lotteries exist -- to raise money, not distribute it. States typically keep about half of every dollar spent on a ticket. On a sheet of paper, show your kids how $1,000 spent on lottery tickets becomes (on average) $500, then $250, and very soon, nothing. Compare this with $1,000 invested in stocks. Growing at 11% for 20 years, it becomes $8,000.
One final exercise might be to help them understand just how astronomic lottery odds are by helping them appreciate how big a number a million is. (The odds of winning any major lottery are usually several million to one.) Have them take a piece of lined paper and number each row. Then have them try to make 100 small vertical marks on each row. Explain that they'd have to fill 10,000 rows with 100 marks to reach a million. If they have 20 rows on each page, they'll be cramming 2,000 little marks onto each page. At that rate, they'll have to fill 500 pages to have 1 million marks. You could point out that a ream of paper is 500 pages - you might have a ream of paper at home to show them, or you could take a trip to a local office supply store or copy center.
If they do fill up a page with 2,000 marks, consider making 25 photocopies of the page. Tape them on a wall and you'll be looking at 50,000 marks. Point out that you'd still need 20 times that many in order to have a million. Boggle their (and your) minds!