You really shouldn't look at it as cracking down. That makes it seem as if he is doing something wrong. It may be a problem. But cracking down presumes an issue of dangerous importance.
For most people the lottery is just a wishful gest of money. The simple idea that it's possible, so why not? To crack down on a gest is to arouse angry feelings, putting undo stress on the relationship.
I think it would be best to treat this as a quirk. A simple oddity that your husband seems to have. It's far safer to treat it as a simple habit than to crack down on it as if it was a criminal activtity.
I would reccomend you starting with the following:
The fact that he likes the lottery so much.
Why it bothers you.
Why it worries you.
Why he should stop.
Possible compromises.
Compromises may include:
Entering the lottery once a week.
Only for significant occasions.
Only when you are both present.
If you win, it goes to childrens college fund.
Etc. etc.
You should ask yourself though, is the lottery the real problem?
Behind most gamblers is a history that begs to be talked about.
Perhaps you are less worried about his gambling with money and more worried about his gambling with life?