So far the biggest issue with disturbing my broody hens is the chick I found this morning stepped on by its mum. I'm guessing it happened partly because I was irritating them and the hatching egg was crushed by her. I've been leaving them alone since finding it.
It happens. That's why we have a "lockdown" phase with broody hatches ... We don't peek until mom gets the chicks off the nest to teach them to scratch. It takes restraint!