A Rite of Passage?

Is it a requirement that every young child do THIS at some point during their toddler years??

Artwork: "Crayola on Yellow" by Miss L.

I gave L a (minor) scolding and they both cried. Must be a twin thing. And I guess the scolding didn't work because some suspicious crayola-like markings appeared on the very same piece of wall some days after...