When my brother and I were little, we used to hide candy from each other in our worn out stuffed animals. We’d have a toy with a small tear in it and pop the candy in there. My mom had no idea.
When we went through (pre-9/11) security in the airport on our way to Florida, my brother’s teddy bear got flagged. Turns out, putting foil covered Lifesavers in a teddy bear is pretty suspicious! But the teddy bear and the Lifesavers alike made it through just fine.
More recently, I went on a trip with my mother and other people. A little girl she was tutoring was going on the trip with us. My mother had made her a pencil case kit to do her homework with, and she wanted to show my mom how committed she was to learning. So she took the kid along with her to the airport without her own mother knowing. It got flagged by TSA, and the poor girl burst out crying when her scissors were taken. She felt awful that she lost the scissors my mother gave her and couldn’t understand why she couldn’t bring her school equipment with her.
Part of the problem is, for people who don’t travel really frequently, they don’t know what to expect fully from TSA, but are better able to adapt to a situation while it happens. It’s much more stressful for children when the rules are suddenly different in a specific space.
Mommy Points has a great guide on how to prep children for security ahead of time. It goes through helping them understand what the process is like and why it’s like that.
My First Airplane Ride is a highly rated book on Amazon for introducing children to what will happen at the airport. It not only talks about the TSA security lines (including why some people will wear their socks), but also introduces all the different people they’ll need to listen to for instructions.