Waterworks has two common meanings that kids might encounter:

1. A system of pipes, pumps, and reservoirs that brings clean water to homes and buildings in a town or city. The waterworks collects water from rivers or underground sources, cleans it, and sends it through underground pipes so that when you turn on a faucet, clean water comes out. Before modern waterworks existed, people had to carry water from wells or rivers. Cities began building waterworks in the 1800s, which helped prevent diseases and made life much more convenient.
2. Crying, especially dramatic or excessive tears. When someone “turns on the waterworks,” they start crying, often to get sympathy or avoid trouble. A younger sibling might turn on the waterworks when they don't get their way, hoping the tears will change their parents' minds. The phrase suggests crying that's partly for show rather than purely from sadness, though people also use it more playfully to describe any crying jag.