Yes, like many things they eat, it’s a matter of dosage. There are plenty of studies that show if a baby chick eats the amount of calcium in Layer every day it can possibly have a harmful effect. The mortality rate increases (that means more of them die) and some suffer internal damage. Some are not harmed. They cut the chicks open to look at the internal organs to determine what damage occurs. I’ve seen studies where they feed the chicks the equivalent of Layer at hatch and one that started that feed at 5 weeks. The results are conclusive, you do not want to feed your chicks nothing but Layer. It won’t harm all of them but it will some.
One bite won’t kill or harm them. It’s a matter of how much total volume they eat in a day and for how many days they eat that volume. My broody hens tend to take their chicks out on the grass practically all day. They will eat some chicken feed but a whole lot of their diet is forage. If I were feeding Layer they probably would not get enough excess calcium to harm themselves since they forage so much. I still consider it “best practice” to not feed Layer but instead feed Starter or Grower to the entire flock with oyster shell on the side. The ones that need the extra calcium for the egg shells generally eat enough and the ones that don’t need the extra calcium generally don’t eat enough to harm themselves.
You cannot keep baby chicks out of Layer if you feed that to the adults. A broody hen will take her chicks to the Layer and take out bits of it for them to eat if they cannot get to it. By two weeks my chicks are flying up to the feeder on their own. Feeding something other than Layer with oyster shell on the side solves this problem.
I agree with the others. There is no need to switch now. If any damage will be done it has already happened. If they forage for a respectable amount of their food it is unlikely they have been damaged anyway. But in the future keep the idea of feeding them something other than Layer with oyster shell on the side in mind. It’s just a better practice.