If you didn't want a child to play with a scooter indoors, wouldn't you put it in the garage? A door from the inside opening to the garage should be set to the alarm to beep, even if the alarm is off. At least, better alarm systems do that. I assume a multi-millionaire's home would be equipped with such.
If someone let Max play with a scooter indoors, he/she's negligent. If someone didn't keep Max from getting a scooter indoors, he/she is negligent.
IMO
How do any of us know for sure that he was playing with a scooter?