Meteorological winter aligns with December-January-February
nautil.us
nautil.us
A better approach is to keep things open - for example, respond with something along the lines of "how do you know?" (or even just "why?"). The you get to talk about seasons and how they relate to temperature and weather, leaves on the trees, snowmen...
I assume different countries will have different meteorological seasons. Just like most countries within a timezone don't exactly sync up with the idea that the sun is at the highest point at noon.