And this is the problem...that turbulence wasn't seen. Passengers were going about their business. I've been on 5 hr flights that had the 'please fasten seat belts' sign on the entire time. I doubt anyone is going to have a strong enough hold on a child, that entire time, to prevent said child from becoming a projectile if the plane drops a substantial amount!!!
Of course, I'm one of those parents that doesn't want to sit, holding a squirming toddler for hours on end!!! For most people that have lap babies, it's an expense issue. If they can get away without spending that addtl money for airfare, they will. And the vast majority of the time, it's all fine. For me, it's just not worth the possibility of something happening. Others can make their own choice.