Half a favour?

One of the days, was visiting and hanging out with buddy and her 2 kids.  I love kids, so I like to be around her 6-year-old son and 8-month-old girl.  The boy was bored and was dragging boxes of toys to play. He asked me to help him.

Boy: Can you reach that box of Lego for me? (box was out of reach from him)

Me:  Ok, sure (handed the box to boy)

Boy: Can you do me a favour? 

Me:  What is it? 

Boy: Bring the box to the other room for me.

Me: You cannot bring it there yourself? 

Boy: No, you've got to bring it there for me.

Me: Ok..... (followed him to another room)

Boy: Next, you've got to bring that (another toy) over here as well.

Me: Why? I've already done you a favour by bringing this one, right?

Boy: No, that is only half a favour. 

Me: ???? A favour is a favour. There is no such thing as half a favour, boy.

Boy: No, that was only half a favour. The other half of the favour is you've got to bring me the other box and then play with me. 

Me: *speechless*

Wow, I'm amazed. Kids are so smart at "negotiating", not that I gave in to his favour (be it half or whole or it could have become a quarter?) because didn't want to spoil him.  I wished I was that smart when I was a kid.  Kids these days... *palm on face* ..... I lose.  Haha!  :D