You might be on to something, but in my experience it's the opposite: parents are overly concerned with their first child then relax a lot by 3 or 4 at which point they barely give a shit, relatively.
There's also the simple limitation that if you have one kid, you can watch that kid like a hawk; if you have four, good luck once they realize they can go in four directions, and you can only go in one.
The solution, of course, is technology and drones ;)
The solution, of course, is technology and drones ;)