Usually the mother looks after her chicks for about 6 weeks. Take them off her too early and they won't have heat they need, particularly at night. Make chick crumb available and shallow water tray, so they don't drown. Left unsecured in a barn the chances are rats will get most, if not all, of them. So they need moving once hatched into a secure unit with fine mesh, which is where they should be now ideally. It's OK letting nature take its course but be aware mortality rates are very high indeed. Our neighbour has been letting his do their own thing for a few years and it seems only two chicks have reached maturity.