Yes, that's true. It does happen on occasion that another hen will attack a chick or try to even kidnap them. However, experience has shown me that more often than not the mama hen will be attentive and not allow that to happen. A lot depends on the temperament of the hen and what kind of mother she is. Just like any species, there's going to be great mama's and poor ones. I've had hens who will not allow her chicks to be within a certain distance of the flock at any time, and others who are kind of careless and don't seem to pay attention. It can go either way, but trying to integrate back into the flock with chicks is much more dangerous in my opinion. If there is a protective rooster, or an aggressive top hen in the group the results can be brutal for the hen as well as the chicks.