It may have been the word "intervention" (as opposed to, say, "conversation") that threw me off. Certainly I agree we should keep an eye out for each others' kids and also that it probably isn't good to expect a 7 year old to wait near traffic for 15-20 minutes (like MM-IL I feel more comfortable about him walking than waiting but of course I don't know enough about the area to judge).
(My mom had me riding a public bus solo to my piano lesson in another part of town by the time I was about 8, and she also got criticized, but she didn't change her plan. At both ends of the trip (getting on the bus and getting off the bus) I was in quiet, residential neighborhoods and of course my piano teacher was expecting me and knew how I was getting there and would have called my mom in a heartbeat had I not arrived promptly. Except in general terms I don't remember this one way or the other though I certainly know I grew up knowing how to read a bus schedule and get places in town that way.)