I don't want to get big

"I don't want to get big.  When I get big, I can't be little anymore."  This was a topic on my boy's mind a lot today; we had to talk about it several times.  I'm not sure what's behind it; all I could think was to reassure him that he'd always be my boy and that Daddy and I would love him whether he was big or little or medium.  He would always be our boy, and he'll be able to do fun things when he gets bigger.  No reassurance.  We finally agreed that he'd stay little, just to keep him from being upset.  Would I love it if he stayed little maybe twice as long as usual.  Sure!  But I won't feed him coffee or anything.  Probably.