Thinking Putty!
I have a child who shredded stress balls, broke mechanical pencils into tiny pieces of plastic, even broke siblings' toys, without consciously meaning to. The best remedy I found was putty. We started with Silly Putty, then found Crazy Aaron's Thinking Putty. Best stuff ever! Only issues were when brightly colored putty got on her blankets. She learned to be careful with it. We've been through dozens of cans of it in the 20 years since she started homeschool. Such a blessing.