A parent will literally be willing to take a child's place before they'll give up trying to save their offspring from death. A normal reaction.
As the parent increased the attack the hawk flew off with the remains of the mockingbird offsping in tow. All the birds, not just the mockingbirds, followed and continued the attack. The mockingbird was the only one who continued hitting the hawk on the back. They drove the predator from our yard.