How can you tell the difference between Mallards and Rouens?

[americana-chick]

I am getting ready to go aand buy some ducklings from Orchalens (dont know if i spelled that right) on Tuesday when they get more Ducklings in. I dont really have any breed in mind but i know that they get a wide variety of ducklings (i looked on Estes hatchery where they get their ducklings and chicks) and they almost always have Rouens/Mallards in one of the bins but dont have it labeled so how can i tell the difference if i end up buying a Mallard/Rouen?
Thanks!

 

[Katy]

A mallard when grown would be much smaller than a rouen, so I would think the duckings would be smaller too.

 

[Funky Feathers]

Yep, Rouens get HUGE, Mallards only get a little bigger than a large call duck.