That's really cute, very good! 
I love overhearing their conversations. Here's a recent one between our ds and his friend (girl), who are 8/9ish years old:
Friend: Is a playdate with me the best time you've had with a girl?
DS: No.
Friend: Who then? (in a very jealous tone)
DS: XXXX came over and we slept together.
Friend: Oh. Can I come for a sleepover?
DS: OK. (in a very "whatever" tone)
At least they're too young to understand why we were trying to look like we weren't listening or interested in their conversation whilst we were laughing out loud inside! (Note to self: no more sleepovers with the opposite sex!)