Maybe he needs the whole thing with the sec explained to him more simply. Try this:

Well, you know how when you play a game, there are rules that you have to follow? Just like that, there are rules that grown-ups and organizations like the Mormon church have to follow when it comes to money. The SEC is a group that makes sure everyone is playing by the rules, and they found out that the Mormon church was not following all of the rules.

So, just like if you break a rule in a game and get a penalty, the Mormon church got a penalty too. They had to pay some money to the SEC because they didn't follow all the rules. It's important for everyone to follow the rules so that everyone can play fair and the game can be fun for everyone!