The ACTUAL reason "Baby on Board" stickers/placards came out was as a safety issue! Not a force field! It has happened in the past where after a serious accident the rescue team looked around and said they had four fatalities, job done....Unfortunately they did not see a crumpled beyond recognition booster seat in the tin-can and had no idea a small infant/toddler was sent through the windshield and ended up a fair distance away from the vehicle! - As a parent (without that sticker mind you) this is quite a fair and resonable thing to do.....To me its as important as "Towballs used for recoveries can kill"....think about it.
Worse case scenario, would you want your own child to be left for the worse and not be properly identified as a victim? Terrible stuff i know but its serious!