My black star rooster named Casanova was like that with my brooder chicks. I to was surprised how he took them under his wing and claimed them as his own protecting them from the other roosters and the aggressive hens. I thought for sure he would kill the little cockerels but they got treated the same as the pullets that was until they got cocky and tried to take dad on.
By then they were almost full grown.
All my chicks are still in my brooders. My free range hens refuse to use the chicken coop I bought them so I talked to hubby about making a slight modification to it to turn it into a half way house for the older chicks until they are old enough so the cats won't eat them when they free range.
Sounds like you picked a good rooster for your flock.
May your troubles be less, Your blessings be more,
and nothing but happiness come through your barn door.