Being raised by hens helps roosters behave well around HENS.
Humans (especially loud fast moving ones that chase) that threaten the rooster's hens/space are another thing entirely, kwim?
They are only 3.5 weeks old. My bantam hens will cover them even at 6+ weeks at night for warmth and comfort (well cover them as best they can).
When they are FULLY feathered they won't need the heat. When they are older they won't all huddle in the nest boxes either. They are just babies, no...