I wouldn’t say it’s a good way… how about plugging in a broken headphone jack- long enough to disable the speakers, short enough that it cannot be removed. Access to sound would require bluetooth headphones.
The kids may also discover airplay and blast the audio over WiFi to the local audio system (there’s a MDM setting “Require passcode on first AirPlay pairing” to prevent that. See https://support.apple.com/en-gb/guide/deployment/dep0f7dd3d8...)