If by 'adult food' , you mean a layer feed, then no. Only actively laying hens should eat a layer feed.
If you are feeding an all flock feed, labeled for chicks through adults, it's fine.
Mary
Mine are integrating as soon as they don't need a heat source, so at five or six weeks of age. They have hiding places, multiple feeders and waterers, and separate coop sections to avoid anyone that's a problem.
So sorry for your losses, time to enhance security everywhere.
Mary