I would not take offense to them "biting you", I think all ducks do this. Sometimes its defensive and other times, it might be to get attention. You have to figure out what it means in your case. I would say the best thing to do is just find ways to get them to trust you more like giving treats and associating you with good things. They might not want to be held and that depends on the duck themselves, but do not take it personally, we want to see them as our babies, but they do not necessarily see themselves as such. Different breeds and individual ducks are different in their likes and dislikes and what they are ok with. Just have to read your little ones and act accordingly. The longer you have them, the more they will get used to you. Just keep in mind, they may or may not want but so much interaction with you even as they get bigger. Hope that helps!