I've found the best thing, Honestly, is when they go through that stange(wich almost ALL ducklings do) is to let them alone, don't push yourself on them, I've had ducks going on about, well, 6 or so years this year, on and off, every single duckling I've EVER raised(from the feed store ducklings, to the hatchery ducklings, to even the few rescued orphans I'd found at the park where my grandpa lives were handled every single day as babies, they all slept in my arms, and in my armpits, LMAO.
My mallards were like that, friendly ass babies, up until the point where they went outside, where they stayed fairly friendly for a few weeks,then they went wild sort of, Boris and Sage were the same,they would eat peas out of my hands, the muscovy ducklings I got at 2 weeks old tamed up really quickly, but it was the same for them once they went outside, and Jumper and Junna I never really fooled with.
BUT now every single duck I've got, Including Jumper and Junna, are super sweet, Albeit they don't like it if I reach for them, but they all follow me around,and let me get real close, wich apposed to a few months ago, they wouldn't even give me the 10 foot rule.
I've found that just being in the pen, and watching them as much as I do, they've grown to know me much better, I let them go about thier lives as they would without me, though i provide food and water.
AND! I bribbed them with...CLOVER, lots and lots of clover :O
now that the spring crop of wild clover in the old horse field is up, and we're not gonna eat it, they get a bucket full of clover in their "pond" every day, and they love it!, so they've quickly come to expect it, and they also come running when they know I've got food.
I love meh duckies.