When my son was in play group, there was a cute poster on the wall that was titled 'The Toddlers' Creed'.

I found it again online. It goes like this:

If I want it, it's mine.
If I gave it to you and I change my mind later,
it's mine.
If I can take it away from you,
it's mine.
If I had it a little while ago,
it's mine.
If it's mine, it will never belong to anyone else,
no matter what.
If we are building something together,
all the pieces are mine.
If it looks like mine, it's mine.

I think this is pretty universal behaviour for toddlers (thus the creed) and I can completely picture little Walter and little Charles acting like this, not to mention jumping on peoples' backs!