Okay. So I guessed there might be a way to sex a duckling by its down color (since there are ducks that have definite male and female coloring), and I also assumed that you could locate (apparently with some work) the actual genitalia. Not sure if that's what you do with your kids hanging around. I know some parents who would (farmers and an obgyn, go figure :)
At any rate, that cleared up that question.
They do look like they're going to be lots of fun. Hopefully they are the females you want and they stay fun throughout.