Again, Check the Clothes Hamper
Obviously, not every place in the world has acorns, so feel free to replace them with something else that holds no value. If it’s smooth and round, your kid will collect heaps of it, store them in their pockets or a bucket, and take them home. Don’t bother asking why they went through all the trouble. Even they can’t provide an adequate answer.
If they could just leave those round objects in a bucket or in the sandbox, that’d be completely fine. But nope, they’re going to dump the contents into a bathtub, onto their mattress, or inside of a pillowcase. Why? Again, you’re just wasting your energy trying to find a motive.