Worried about my rooster and ducklings

[HarveyDay]

We got two ducklings a couple of weeks ago. They're about 3 weeks old and living in our house in their little box but growing rapidly and the time to move them outside is rapidly approaching. We didn't make any introductions to our flock the first week but this week I've been letting them run around while I clean out their box. The hens pay them no mind whatsoever but several times our rooster has run at them and I've had to separate him. Eventually, I'm going to have to leave them out unsupervised and I'm worried that the rooster is going to hurt them. Any suggestions?

 

[sourland]

I would not leave them with him unsupervised until they were far larger.