Here are some seasonal science ideas - perfect for a long, cold vacation day with your own kids, or when your school kids need something fun to break up the sometimes-long stretch that is January and February.
Activity #1 - Hot Chocolate Solubility
You'll need at least two different varieties of hot chocolate mix and one mug for each variety.
Place an equal amount of mix in each mug. Add the same amount of water to each mug (it would be good if you could have one person add it to each mug, so it all gets added at the same time). Stir the contents of the mugs (at as close to the same rate as possible), and observe.
Does one variety dissolve better (faster) than the others? Hypothesize what makes the difference.
Activity #2 - Hot Chocolate Taste Test
Since you acquired a few different varieties of hot chocolate for activity #1, you might as well put them to additional use....
Before you prepare the hot chocolate, create a list of properties you find desirable in hot chocolate, as well as those less-desirable. Possibilities include: sweetness, chocolatey-ness, creaminess, bitterness.
Prepare each variety of hot chocolate according to its directions.
Sample one variety at a time and evaluate it on the properties you listed, giving it a score for each property.
Once you've sampled and evaluated each variety, analyze the results to see which properties your favorite hot chocolates have in common.
Activity #3 - Are Marshmallows Good Insulators?
Prepare two identical cups of hot chocolate (same variety of hot chocolate, same amount of power, same amount and temperature of water) in identical mugs.
Float enough marshmallows on the top of one of mugs to completely cover the surface.
Place a thermometer in each mug.
Observe and record the temperature of each mug every few minutes.
Do you notice any difference between the two mugs? What do you think accounts for that difference?
If you're looking for some additional activities....
the Sugar Cube Rate of Solution activity and the Goldilocks & the Three Bears Heat Transfer activity could both be adapted for use with hot chocolate.