We are talking about if the hen was to accept the chicks.If chicks are raised by a Hen the Rooster won't bother them. Tossing in 3 week old chicks can be a nightmare.
Yes the chicks are probably to old but you say you wouldn’t put them in with your rooster. Personally my friends and I have all had roosters who loves taking care of the chicks while the mother hen was off eating or something. So next time I would say with younger chicks to not be afraid to keep the chicks with your rooster. If he is acting aggressive than remove the hen and chicks. I wouldn’t want me to be responsible for letting your babies get hurt.Good luck