Handle them as much as you want! I entice my ducklings with treats, (kale, lettuce, peas, carrots, grass). If you want friendly ducks, they need to be handled regularly. With my own, I often let them out of their pen to run around in the family room. (make sure the door is closed so you can control where they play, and so any other animals leave them be.) I find that the most helpful way to interact with them is for me to sit down on the ground with them, they'll run around, and make noise-they'll want to try to eat anything they can and look for anything fun to peck at.
I have two babies right now, and they tended to run away when i want to pick them up, so each day I started seperating them. (they'll cry for each other, but it's fine) I left one in their pen, while I took the other duckling to the other side of the house where they couldn't hear each other peeping, I sat on the floor with him and once he calmed down a little, he climbed into my lap, and snuggled into my arms.
Just remember to have a lot of patience, because some ducks will take much longer than others, with my ducks they like to be petted, and held but ONLY IF THEY GET TO CHOOSE WHEN.

Let them come to you, mine still hate to be picked up but once they are there they seem to love the attention.
P.S. entice them with a bath! I started putting mine in the water (used our sink) to swim when they were one week old. As long as you're watching them (they can easily drown) then they'll be okay-once they start to shiver, put them back under their heat lamp.

good luck!