Painting a Holiday

I scored some very large cardboard panels from Ken our custodian, perfect for Christmas murals.  We painted a fireplace with a hearth, with Santa coming down the chimney.  The kids are painting their own Christmas tree, as real trees are not allowed in school.  I had no idea this activity would be so much fun with the kids really getting into the holiday spirit.  They are totally absorbed.  At times I have to bite my lip to keep from telling them to do it this way or that way.  I want them to paint it their way.