Re: jingshangling to simatai worries
about 50 people do the Jinshanling - Simatai walk every day. Mostly tourists, mostly not well trained hikers.
I would not hesitate to do the walk with a 7-year-old son. Take plenty to drink and walk early so you have enough time for some rests. I assume the walk will be great fun for him.
There is not a single dangerous step on this walk. A suspension bridge is a suspension bridge. For me it was part of the joy.
From Simatai it is easy to get to Chenge. Taka a taxi from Simatai to Gubeikou, from there busses run frequently to Chengde. You should be at Gubeikou not much after 12:00. Chengde is marvellous.