What are they??

[learycow]

Wow - thanks for all of the input - I am looking forward to some beautiful muscovies. Here is a few more questions I have - I have heard that ducklings can drown if they try to swim too soon - when can they play in the pond, or is that a myth? When will they no longer need the hen as a foster mom? Also the lighter colored one is getting a lot bigger in body size with thicker legs and bigger feet than the darker one - could this be because one is a drake and the other a hen?

Yes, as they grow the drakes will get thicker/larger legs and necks. And eventually it will be obvious as the hens will be smaller overall.
They can swim when they are little, but I wouldn't recommend a pond. Use a sink in your house, bathtub, or a shallow tub/grain bucket. They can swim and will play around, but before they are fully feathered their down will absorb water. If left unwatched, they can get waterlogged and drown. Or if they aren't put in a warm, dry place after their swim they can get chilled easy.

I have had hens raise them until they are 3-4 months old. But you can take them away any time. If it's warm outside, then they won't need a heatlamp. But if it's still chilly like it is here in Maine (not about 55 degrees during the day and in the 30s at night), then I would leave them with the hen or put them inside a coop with a heat lamp for warmth.