Have you heard of the panic room system? It requires a sectioned off space until the chicks are around three months old. The chicks will spend a few days during the day time in the safe area so they can observe and be observed by the older chickens.
Then you open chick size openings in the enclosure so they can go and come at will. Food and water remain inside the enclosure so they don't have to compete for these.
I and many others here raise our chicks along side the adults from day one, and at two weeks, the chicks are safely mingling with the adults.