My party was together. We all stepped through the security line together. My friend had a stroller and a 6-year-old and was right behind me, and as I stepped forward after being cleared from the bag line, she was directly behind me with her bag and the 6-year-old. Her eyes weren't glued on me, so she didn't see that I was whisked away and I didn't have time to tell her.
Luckily, as I said, it wasn't super crowded and I was able to keep my eye on them and reunite quickly after going through the metal detectors, but it could have gone differently in another situation.
Not giving people a split second to say "Hey, I'll meet you behind the metal detectors on the other side of the entrance!" as they're dragged across the entrance plaza isn't great and that extra split-second doesn't do squat for security, all it does is separate people from their children for no reason.