I mentioned it to my kids and they were like,

"What's 9/11?"

"Islamic terrorist attack on US soil."

*blank stare*

"It happened in 2001."

"Oh, it's something historical. Like the Berlin Wall coming down. Or WW2."

"Terrorist attacks on US soil used to be a very usual thing. Everyone was really upset. It was a big deal. It's why we can't take big shampoo bottles onto planes, anymore."

"Oh, okay. You used to be able to take shampoo onto planes?"

"Nevermind."