When the children have completed the coloring, instruct them to crumple and flatten the paper bag again and again until it is soft and wrinkled like a tree bark might be.
(the children; have completed; the coloring) (it; is; soft and wrinkled like a tree bark) (it; wrinkled; )
the children it it
have completed is wrinkled
the coloring
soft and wrinkled like a tree bark