I did try sunflowers in very small quantity the two times I had to get them in the pen to leave the house.Sunflower seeds are fine in small quantities as are small pieces of strawberry.
I think you would be shocked at what mum tells them is okay to eat.
I used to feed chicks just a few days old finely chopped cooked white fish with mums permission of course.
Chipie took the seeds away from me and fed them to the chicks.
They didn't choke, which was my fear

Théo isn't the chick's father. The eggs come from the same farm as him and Chipie.I don't know enough about the keeping arrangements, who mated with who etc etc to know anything useful.
Is Theo the chicks father? My appologies if you've covered this but I can't remember if you did.
There is way enough space that Chipie could stay away from him and the flock but it's not what she does. She goes right where they are and make broody screams if anyone approaches.The hens have attacked her, but way less than before she had the chicks. Théo attacks her and the chicks when she comes too near.
I don't see what I can do except try to let them sort it out and make sure the chicks escape. The problem for me is whether he will tolerate them in the coop when the time comes.
Pretty offender tax