A couple grafs from NSA's page for kids:
What’s cryptology? Cryptology is making and breaking codes. It’s so cool. We make codes so we can send secret messages to our friends. And we try to figure out what other people are writing about by breaking their codes. It’s a lot of fun.
On this site, you can learn all about codes and ciphers, play lots of games and activities, and get to know each of us - Crypto Cat™, Decipher Dog™, Rosetta Stone, Slate, Joules, T.Top, and, of course, our leader CSS Sam.
You can also learn about the National Security Agency/Central Security Service - they’re America’s real codemakers and codebreakers. Our Nation’s leaders and warfighters count on the technology and information they get from NSA/CSS to get their jobs done. Without NSA/CSS, they wouldn’t be able to talk to one another without the bad guys listening and they wouldn’t be able to figure out what the bad guys were planning.