I agree with Tara. I have a 4 (almost 5) year old, and we're doing Cultural Geography this year. Talking about maps, continents, countries, and peoples. Making food from different countries. Reading some books about different countries. I'm not too worried about it because I know we're going to cover this stuff again with our history and geography, but it gives us some structure and "practice" at doing school. I have a 3 year old, too, and he follows along, but it means less to him than to my 4 year old.
Here are some links to a couple of the ideas I'm incorporating (both these ladies are/were posters here):
Hazel"nut" Academy's Countries/Cultures
The Sunny Patch's Countries and Cultures of the World