I finally found this after a long search…
“Toddler’s Creed” by T. Berry Brazelton
If I want it, it’s mine.
If I give it to you and change my mind later, it’s mine.
If I can take it away from you, it’s mine.
It I had it a little while ago, it’s mine.
If it’s mine, it will never belong to anybody else, no matter what.
If we are building something together, all the pieces are mine.
If it looks just like mine, it is mine.
Wow, this kind of reminds me of some grown-ups I know…