Thankfully, with a little practice, most species of waterfowl aren't hard to sex. Yes, most of the time its obvious as they feather out due to color, but not always.

Like with the goslings, they'll continue to be similiar in color and stature.

I sex them in a way that is pretty close to popping ball pythons. With the proper technique, you can evert the organs of a male from the vent and therefore verify sex.

Here is a good link that demonstrates:

Goose Reproduction