I accidentally went through security with my infant son's boarding pass, separately from my wife and son who went through with my boarding pass, the TSA agent only checked my wife's boarding pass and not my son's. Not to mention how trivial it is to get liquids on a plane without them being searched. Bruce Schneier notably went through security with two of the biggest bottles of saline solution for contact lenses he could buy without them actually searching the bottles. When asked by the TSA why he had two bottles he told them "two eyes" and they let him through. Not to mention he was using a forged boarding pass at the time to go through security.

https://www.schneier.com/news/archives/2008/11/the_things_he...

My wife was also wearing my son in a wrap at the time and just walked through a metal detector, no searching pockets or taking off the wrap or anything like that. Anyone trying to sneak contraband through could just carry it through with the baby knowing it won't be searched and then just leave after exchanging the contraband past security and walk out. You could easily sneak 10lbs worth of contraband through so long as it wouldn't set off the metal detector.