Is there any child protection for the domestic long-distance bus tour of the elderly tour group?

There is no explicit provision, but generally people over 70 will ask their families to write a certificate to prove that the elderly are healthy and can complete all the tours by themselves. If there is any problem, it has nothing to do with the travel agency.

It is normal for travel agencies to ask for these certificates, which is also a kind of risk avoidance for you and the travel agency. After all, when going out, the first thing to pay attention to is safety.