In that sense, Linds, everything's preventable.... right? "What if I had just stayed in the right lane, then I would never have hit that car...."
My point, that you quoted, was that accidents happen, and nothing is 100% fool-proof. We can outline hundreds of what-if scenarios that may not be likely, but may be possible in causing a snake to get loose, again, "despite our best efforts." Supports break and enclosures fall - snake may escape.... etc, etc.
You also touch on common-sense in your post, while I agree that this is all that is required to prevent an accident, with humans, this sense is rarely as common as you'd think (hope).
My point is simply that the one and only 100% way of ensuring a child is not put at risk is to remove the possible risk all together.... right?
This is extreme and is not necessarily my stance, I have serpents and I have kids in the house....
I would never be so arrogant to say that it could never happen, it certainly could but probably won't. The girl-friend likely doesn't want a child's life depending on "probably" when larger constrictors are involved.
But to each his/her own of course.