I rescued a duckling about 2 years ago. I paid $5.00 for it, as it had been given as a prize to a child, and I didn't want the child to end up with nothing. It was being raised by itself in a fenced yard with no pond. It appeared to be a female mallard. I put her in my neighbor's pond with a big white semi wild Pekin, that was given to me, but I haven't seen the Pekin in over a year, as they relocated to the creek, and roamed as they saw fit. I fed the mallard all winter last year and she was gone most of the summer with wild ducks, who fly off the minute they see me, but she isn't afraid. I'm hoping if they go somewhere she will go too. I fear she is too tame and trusting. My advice would be to get them with other wild ducklings and hope mother can't count. I know that I probably broke some law, as I can't prove that the duck I rescued was owned legally by the child, or the people that gave it as a prize. State departments of natural resources can be pretty prickly at times. In Ohio, you have to have a permit to rehabilitate wildlife. I would do the same thing you have done so far.