<human>: Can you provide a brief rundown of the text in within 3 sentences?

My friend from out of town came by to stay at my house overnight on a weekend trip with his family. It was my friend, his wife, and his 3 kids (aged maybe 6, 4, and 1). We had a great time, went swimming, grilled some food, played board games and wore my dog out in the backyard.

I collect [Dunnies] and these kids went nuts for them. I gave the two older kids one a piece since I had a few duplicates and they later gave me 50 cents apiece for them (unexpected).  At one point the kids decide they want to trade the ones they have for different ones, no problem. They trade them out and off they go to play. After a board game it's time for the family to drive back home, I get hugs and high fives and I spend the rest of the day resting. 

The next day I get a call from my friend that the kids snuck the figures they traded out into their bags as well as the ones they kept.  My friend says he's sorry, his wife is embarrassed, and they are going to send all four of them back along with letters from the two kids. I told him not to be embarrassed, I went through a petty theft phase but I was a bit older and almost went to juvie for it. I figure if they learn this lesson early and with someone who won't try to scare the shit out of them, this is a good time to get this out of their system.  I said I would send back the dollar that they gave me for the two original figures but he says no. I really don't think I should keep their money since they aren't keeping the figures that they paid me for.  I haven't received the letters yet as this just went down but I could use some reddit wisdom on what to write back to the kids to sink in the idea that stealing is wrong but they are still good kids and are welcome to hang out if they mend their ways.
<bot>: Friend's kids took some toys after saying w/ me for the weekend, got busted by their dad.  I need suggestions for a response letter to the kids telling them why stealing is wrong.