Glad you received the money owed. Hopefully, both you and kid learned a lesson. And I'm glad the parents did the right thing.
Lessons for the rest of us:
1) Do not do deals with children/minors.
2) Do not ship without delivery confirmation/tracking of some sort.
3) Never agree to accept a split payment on Paypal.
(#2 and #3 void all seller protection on PP. #1 is just plain foolish.)