Eggs are fine - it's what they eat while they're developing and hatching anyway
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If they're 13 weeks and have had any sort of time on the ground, or if you've given them any grit, they can eat pretty much anything a grown chicken can eat. Plus the more variety you offer them the more likely they are to accept new foods later. Meat is ok (extra protein) - fish, chicken . . . just don't go nuts. They should still get a majority of their food from the grower feed since it has more balanced nutrients - but offer them fruits, greens, bread, yogurt . . . whatever leftovers you have. Stay away from avocado (although it's not 100% determined to be toxic there is some speculation). Just bring it on and see what they like - you'll be amazed at the little chow-hounds.
I have a little compost bucket by my sink. Now I will add a little bowl for chicken scraps. I wanted to mainly make sure they were old enough for treats and which items to avoid completely.
Did you mean your chicks are 13 weeks old, or that you have 13 one week old chicks?
Good point!
IMO very young birds should eat their crumbles, every mouthful is important when they are growing very fast; by a month old I give a rare treat and provide grit if necessary; then by 4 months, I'm more comfortable with clean scraps from the kitchen and free ranging to eat grass, etc. They are still growing very slowly, but I feel eating their fresh vegies is as important as the commercial pellets fortified with vit/minerals.
Though I do wonder why I am so careful about giving unspoiled food when so many head for the compost pile to check out the spoiled scraps thrown in compost!