Can 4-5 week old chicks eat apple cores/seeds/peels ?

Yeah, within reason. Don’t overdo it for a few reasons.

First, they need to have grit to digest the apple seeds. As long as they are getting grit they will be able to digest them. I doubt the apple itself will cause a problem and probably not the apple peel, but definitely they need grit for the seeds.

It’s best not to feed them a whole lot of any one treat. A general rule is that they should be able to clean it up within 10 to 15 minutes. This way it is does not disrupt their diet and they still get a balance of nutrients. Also, think what it would do to your digestive system if you ate nothing but apples for a day!

The other thing will panic some people though there is no reason for panic. Apple seeds like many fruit seeds contain cyanide, a poison. Before you freak out, there is not enough cyanide in one apple seed to hurt them at all. I swallowed a lot of apple seeds growing up on the farm, just picking apples up in the orchard and eating them and I’m still alive. Many other people have done the same. Chicks are a lot smaller than humans so it won’t take as many seeds to hurt them as it would a human, but it still takes a lot. I don’t know how many chicks you have or how many seeds you have, but I’d probably avoid piling a lot of seeds in there. Some won’t hurt them and I can’t tell you how many “some” is. Don’t stress out about a few, just don’t give them a big pile.

Since you made apple pies, you probably don’t have a huge pile, but I don’t know how many pies you made or how many chicks you have.

I have absolutely no problem with the chickens eating apples in my orchard and I’ll throw a few apple cores to them, seeds included. But when I make apple sauce or such, I don’t give them a huge pile of seeds. Reasonable precautions.

The harder food is to get ground up in the chickens gizzard determines what I would give them. 4-5 weeks is quite young to be giving such food as apples, especially if you don't sprinkle a little chick grit on their starter feed. There's few nutritional benefits in apples for chickens anyway. I will toss some tomatoes, chard, and kale to them from the garden every so often when they are adults and they range for greens. Even grass should be mowed because chickens can get impacted crops from eating too much, or long stockier strands of pasture grasses. Less variety is better when they are as young as 4-5 weeks. They are growing and developing, so you want a good quality starter feed to be consistent nutrition for them.
 

Would they be OK with that many chicks and that many seeds? Probably. But I think reducing the number of seed was prudent.

Yeah that is just fine, 

Just don't do this daily...:D

Coco Rae