I think the main issue is the feed they each need. Chicks need starter feed until 18-20 weeks of age to give them optimal conditions to grow. Adult chickens, especially laying hens, need the layer feed to give them the extra calcium their bodies need for producing good eggs and maintaining their health. Chick feed doesn't provide the calcium layers need. Layer feed has too much calcium for growing chicks' digestive systems. So it's best to keep them apart so they each can have only the feed they need.
Older chicks can be let out to free range with adult birds, with supervision at first to make sure no one is getting picked on or pecked at. But keep their feeders separate until the chicks are 18-20 weeks old.