What Would a Child Psychologist Tell Me?

I try to encourage Maya's creativity. We bought her an easel, paints, and markers for Christmas. Tonight, Reili wanted to join Maya with her "art". I thought it was sweet that Maya was tolerating her little sister. Reili was not screaming or even crying out in pain, so I turned my back (yes, I know big mistake) and let them "play" together.

Maya came out with blood on her knee and a sad look on her face... except it wasn't quite sad enough. I didn't believe it. Yes, it was red (washable) paint. Her sister/partner in crime was slathered in red, too. Here are a few pictures.

Maya even posed for the pictures while Reili kept saying "cheese" while smiling for the camera. I'm wondering at what point to stop encouraging her creativity....