I got four new baby ducks about two weeks ago and I'm struggling to get them adjusted to their new home/life/myself. One of the ducks have bitten me ever since the first day but now another has picked up the habit as well. I'd like to break this habit as soon as possible because I'd prefer to not be chased and bitten by a full grown bird.. They also seem to still be a bit anxious and afraid. Whenever they see me they run to the opposite side of the pen and if I reach inside they go into a panic.. I want them to feel comfortable with my presence but I'm not really sure what I'm missing. Any advice or tips would be great. I'm having trouble finding anything online.

Also; I'm not sure how to sex my ducks either? I've seen online that their calls/quacks are different for males and females (similar to Guinea Fowl) but is that the only way to sex them?