I normally just add different things they can explore and climb on like sticks, branches (best when they have leaves in them), and rocks. If your chicks are in a brooder though these won’t really work. I have never raised chicks in a brooder before so I have no idea about entertainment for chicks.
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When they are about 1.5 - 2 weeks old, give the a chunk of sod from the yard, grass, roots, rocks and all. They will initially be terrified of it but then will have a blast digging it up.