# who kills the prophets and stones those sent to you

"you people who kill the prophets and stone those whom God has sent to you"

# How often I desired

"I have so often desired" 

# to gather your children

"to gather your people" or "to gather the people of Jerusalem" 

# the way a hen gathers her brood under her wings

This describes how a hen protects her young from harm by covering them with her wings.