What's your set up like (photos will help)? Ample space and ample clutter give chicks a better chance at getting away from adult bullying.
How long have the hens been able to see the chicks without access? "See but don't touch" isn't an instant process - it can take a week, it can take several weeks.
Do you have multiple feeders/food sources and/or waterers available? A lot more aggression happens around resources like food.
Do not introduce 1 by 1... the chicks stand a much better chance as a group, as they can scatter and run if the hens go after them.
How long have the hens been able to see the chicks without access? "See but don't touch" isn't an instant process - it can take a week, it can take several weeks.
Do you have multiple feeders/food sources and/or waterers available? A lot more aggression happens around resources like food.
Do not introduce 1 by 1... the chicks stand a much better chance as a group, as they can scatter and run if the hens go after them.