Disable volume buttons

Hi Experts, my son usually takes my mobile to view youtube videos and play games with full volume. I installed volume locker and it works perfectly but when he presses volume buttons to increase, he can see its not increasing and causes havoc :). Is there anyway i can reduce the volume level and when he presses the volume keys, either full volume is shown or nothing is shown at all (till we disable the app afterwards)

Please any idea ?

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