Babies Killed By Mum

i have a female who killed her 1 week old and 2 day old chicks

the where okay night before  but this morning they where both dead with peck marks on their heads

i dont touch chicks until they are at least 4week old for fear mother may reject them so i know it was not that

please help ive taken her out of my breeding program  she was such a good mum until now