Play Dress Up
Get out the Halloween costumes and the uniform you saved from your first job at a diner. Let your kids dig through a pile of hats and scarves and anything from 1982, and see what sort of things they come up with. Even those too young to get into rhinestone sunglasses and tiaras can have fun putting on and taking of an extra-large hat or stomping around inside wearing rain boots and dragging an umbrella.
Put on some tunes and bust a move. One of the worst parts of being stuck inside is the pent-up energy. Teach your kids to pop and lock, do the running man, or even do-si-do. Note that this can be especially fun when combined with Activity #11.
Make an Indoor Winter Wonderland or Carnival
Pull out the cotton balls and have a snowball fight. Afterward, use those same cotton balls and glue to make snowmen. Or, create an entire indoor carnival, complete with beanbag games and stickers for prizes. Toothless carnies optional.
Engage in Retail Therapy
No actual purchasing required. Check out the local bookstore, where there might be a story hour. Or, run around inside the warm mall – many malls have a toddler-friendly play area. Since malls often open before the stores open, morning people (or those forced to be awake by an early riser) can hit the mall and just walk around.
Try hands-on science experiments using stuff you’ve got in your kitchen. Polish old pennies with lemon juice or watch yeast grow and fizz. Younger kids can see who can blow the biggest bubble out of wands made of homemade pipe cleaners dipped into your own bubble solution.