He knows

Tonight we told Buddy about Santa.  There was an incident on the bus where Princess came off in tears,  so we decided it was time.

I've been dreading this day for a while.  We used this letter as a way to talk to him about it.
http://www.cozi.com/live-simply/truth-about-santa

Though bitter-sweet,  I think it went over better than I expected.  At least for me. And at first, Buddy had a lot of questions,  and was sad.  But when he found out he could help us go Christmas shopping for his brother and sister, and help us wrap presents and move our elf,  Wyatt, he got SO excited :) He even said that he didn't want presents because he'll get joy in seeing Princess and Monkey open theirs.  He also offered to help pay for the presents,  but was quick to add that he doesn't get much allowance so he's not sure how he'll do that!  Smarty pants ;)

I guess we'll see what questions come to him in the next few days.  And hopefully Christmas will be just as magical for him.
It was a sad and difficult door to close,  but I'm excited to see what opportunities are in the newly opened one :)