Usually she finds something to do while we are sketching. She also draws or if outdoors, she is happy playing treasure hunt in an empty plot, but, as we are not quick sketchers sometimes she gets bored. She knows we are having fun (just like kids) and she never complains about it, she just puts on her "bored face" and waits for us to notice it.
Then I say "ok, stay still... I will draw you!" and this always cheers her up and gives Mário a bit more time to finish his drawing.