Hey Nate! I’ve got three kids myself — though they are grown up now. Kids love destination hikes. As you noted, hikes with water are always a big hit, but it can be other things too — like a historical site or something fun.
The old LA Zoo in Griffith Park comes to mind, as do the ruins of the old cabins in Icehouse Canyon. Don’t worry about trying to get to the “top” (whatever that is). Just have fun, and explore a little further as their strength and curiosity grows.