Family with 2 kids 8 + 10 years, visit the not so tourist part off the Wall and do a toboggan ride

I personally recommend you visit Jinshanling. It reveals the wild beauty of the Wall and there won't be many tourists generally. There are special buses to Jinshanling near the Exit C of Wangjing West Station of line 13. From Xisi Station, you need to transfer twice.
Do you mean doing a toboggan ride on the Wall? You'd better not do it for your kids' safety.
There is a Jinshan Hotel at the foot of the Wall. You can view the sunset on the Wall and stay there for one night.
Hope your enjoy your time!