**but what mother can keep a constant eye on an active 9 year old boy? **
The kind that takes protecting her children seriously?
I know I wont change your mind but I will give you my thoughts on the subject.
The old children become the more independence they want. As a parent you have to use your judgment to decide how much independence they can handle.
Making that judgment requires experimental testing on the parents part. The parent yields responsibility to the child and sees how they handle it.
Eventually you have to trust the child out of your sight. If you do not your child will rebel, become overly fearful of the world and/or become narcissistic.
Certainly there are great dangers in the world for a 9 year old. But you can not totally isolate him from the world. He must be taught to negotiate the dangers on his own. You will not be there all of the time.