Government is a body of elected officials which help run a country. You can also explain the importance of voting and the electoral college. I'd also explain how all 3 branches work, and are selected.
Politics is hard to define. I usually define it as a party system, where each party holds a core set of values. (Assuming we're talking about American politics) You can explain the two major parties, and maybe some of the less heated opinions of each. Taxes, spending, something along those lines.
How old are your kids?