We have RVd in a motor home with kids in car seats. I do think that advising parents to take kids in a separate vehicle is completely unrealistic. Most campgrounds charge for extra vehicles, if they will even fit 2 vehicles per site. If you have a class A (bus), there is a good chance you won't be able to even fit a second vehicle in your campsite. Then there is the whole issue of why take a family vacation if you aren't going to be together as a family. IMO most of the people who say take two vehicles aren't RVers themselves.
We have had motorhomes with TAs so it is possible. Where you stow things can make travel safer too. Yes, there is a chance of a rollover, but that situation wouldn't be pretty even if you were towing OR if you had a fully stuffed minivan. JMHO
We prefer towing either 5th wheels or trailers for reasons other than the car seat situation.
I personally think the biggest issue with RVg is not the car seats but rather driver inexperience and inability. Driving a class A or towing 35' is not for the average driver. I think people should be required to take a special test to drive these things. Here, you only need an extra rest for over 35' or air brakes.