For autistic children, being forced to stop stimming can be harmful and even traumatic. A child shamed out of stimming will carry that shame throughout the rest of their life. They will learn that they are only allowed to show their emotions when it is deemed socially acceptable. Unless a stim is dangerous, you should not force an autistic child to stop. Even if a stim is dangerous, or just disruptive, offering an alternative can be a better way to provide similar stimulation.