Do you have any way that you could catch them like a net or anything?
I would just let them be raised the way they have always been raised and then catch them when they're older.
Maybe make some sort of cage that opens in the top so that it's easy to put them in.
I haven't even been able to process any of my chickens because they all sold

I do have one cockerel that's in my layer flock right now that I will have to process. It was born on Halloween, but it definitely isn't big enough yet. The only reason it is with my layer flock is because it snuck through the fence