I used to raise Mallards and a few other gamebird species. The babies imprint on whatever they see so it's possible they'll be more tame then wild mallard babies. But don't expect them to enjoy being held or petted when older. I started off with a pair I bought as adults from a game farm in NJ. I clipped their wings the first year I had them. I kept them in a 40'x60' garden surrounded by a picket fence. I had a small, 500 gallon pond in the middle. They bred and had babies, the babies grew up and flew away in the fall that year. The following spring they had babies again and I let the adult pair molt so they could grow new primary feathers. They all flew off in the fall. Lucky for me I had a very nice lake down the street from me that is spring fed and never freezes. My guess is they stayed there during the winter. Everyone walks around this lake and feeds the ducks so they would be well taken care of during the cold months. In the spring my female few back to my garden pond and had babies their. She did this 7 years in a row until my parents sold that house. Keep in mind I fed her the whole time she was their. I'm not sure if she stuck around for the new owners or not. Anyways, hope this gives you an idea of what could happen. If you want a super tame mallard then you'll have to hatch it from any egg and let it imprint on you.
