It can at times really depend on the temperament of the drake. I always put the ducklings in their own pen beside the adults for a few days so they can see each other for a while before putting them together. Usually mine are ore like 6 weeks old when they move outside. the drakes- and some of the older ducks as well will give them a nip at times but if it gets too much I put the babies back in their own pen for a few days more. Your drake may be really good with the babies around- or he might attack them- at 4 weeks they are still too small to have a good chance of defending themselves- so its a good idea to closely monitor them for a while when you put them together.
he stands next to the fence all the time seem to be watching over mother and babies. but the pen hes in now my other duck just hatched 9 today an haven't come of nest yet .so i will Ive to try and fence them in or move him in with the 4week olds.thanks for replay