Sorry but 9 is plenty old enough for a child to ride their bike unsupervised. It is also plenty old enough to go swimming. I was swimming by myself at our local rec center by 4th grade.
The only way that a parent would be negligent in this situation is if they knew their child was a retard about traffic/safety issues or that it was an unsafe environment to ride the bike (like times square or down the side of a highway).
The children were riding their bikes down a sidewalk and not the road. So it sounds like it was a perfectly safe environment for them to be in.
My only questions about the situations is how much space was between the road and the sidewalk and was the bike owned by the family or rented from Disney?
From earlier descriptions of the accident it sounded to me that not only were they on the sidewalk but it sounded like there was a buffer of space beten the sidewalk and street, like a strip of grass. From the link in this blurb itsoundtome like the sidewalk was right next to the stree
I don't even consider the flat tire to be a part of the problem. Unless there
was a sudden blowout, an already flat tire would not have caused him to lose
control. If it was a blowout, well what can you say? Accidents happen.
The two most likely catalysts were either the boy did something wrong or iwas a freak loss of control. Since no one else was there in the boy's shoes, no one can say his was doing something dangerous/wrong.