Grab some paper and a drawing tool and.....
Cover a page with shapes, all of one type or a variety. Let them overlap or let them float free and touch nothing! Make them a variety of colors or limit yourself to only one. Now color in a few or not. Use different types of lines to make your shapes, curvy, broken,zig zag,etc.
Grab a page from the newspaper and draw a picture on top of it. Use lots of detail and ignore the newsprint. Add some color. Try a new medium if you have it available.
Illustrate a passage from a book or a poem.
Divide a paper by folding it five times. They do not have to be perfect folds and can be horizontal, diagonal, vertical, etc folds. Now, use line and pattern to fill in the spaces. Google Zentangles if you want some ideas.
This is the most fun idea, yet! Grab the entire family. Give everyone a paper and something to draw with. Set a timer for five minutes and tell everyone to draw anyway they want on the paper. When the timer goes off, pass the paper to someone new and continue to draw on the new paper. Continue in this manner until everyone has contributed to every paper. When you are finished, add color to the paper you started with.