Every season of the year is full of opportunities to get children outside where the hands on learning mode can kick in at full blast.
Most children will recognize that winter weather is colder than the other seasons. Even in mild climates spots like Sacramento it's colder. It's the reason they have jackets, hats, gloves, and scarves.
Get them outside. A little geometry never hurt anyone. Some simple math thrown in, without them even knowing it? Sure.
Pick a time of day when the sun is about as high as it's going to get for the day. Pick a spot outside. Have your child, or if you are a teacher, the children in your class, stand with their backs to the sun. Mark where the length of their shadows end. That's it.
At the end of the week, if you did this on a Monday, out you go. Do the same thing. Measure the differences between the shadow lengths. Do this a couple of times each month of winter.
Chart it. Put it up where it can be seen. The questions will come. No need to ask much. Curiosity will kick in. Write the questions down next to the chart. Sooner or later one of the children will tumble to the reason the shadows are getting shorter, after having spent autumn getting longer.
This is where the discussion kicks in. Painlessly, you have presented math, geometry, language, and if you're really good, art, into the simple business of going outside on a regular basis and observing the natural world. Not bad.
The only question is this: Will you do it?