It really depends on the hen why they do that. Some just need some time to get use to their chicks chirping and sight. We had one hen, however, Wynona, who tried to kill any chick she saw but adored them when they were tucked under her. It's like she thought rats were trying to eat her eggs. She was very bonded to her eggs but freaked out at the sight of anything moving and would peck at them and throw them around. They all survived, but I had to take them from her and find her a new home so she would break-up.
Some hens will kill chicks if they don't like the color of the chick, they may also do it to a weak chick they are trying to help stand or free from it's shell. Some also attack chicks that are given to them when they have only settled onto eggs for a week or less (when they still expect eggs for a while) or if they are nervous, too hot, hungry, or thirsty.
I would try taking any newly hatched chicks from her until they are fully dry and able to walk around. Slip them under her and watch her for a short distance (so you can stop any attacks). Once the chicks can walk and chirp they'll usually tell their mom to be more gentle.
Yea I took them as i seen new ones.there was three fully grown in eggs that were dead..it may have been just to hot out.we've been having high humidity and in 90s to 100 all through that time and coop was probably even hotter..