There are so many problems with this, and the reason why a bunch of the cases on TCAP were thrown out.
1. These "children" initiated the chat by stating their "ages" online. They are in adult chat rooms, not child chat rooms. This right here is enough proof to show that the adult wouldn't have done it otherwise. After all, why go to what should be an all adult chat room to find a child? Makes no sense at all.
2. There is no real child involved. Just like you can't get in trouble for growing fake pot, you shouldn't be able to get in trouble for talking to fake kids. Chatting with someone you "think" is a child, and know this only because of the text "13/f/CA" on a screen does not a pedophile make. You actually have to have a real child involved before a real crime has been committed.
3. Since it is an adult chat room, the adult could easily make the case that they were "roleplaying." That is a very common thing in which two adults will take on "roles", sometimes one a maid the other an owner, one a doctor the other a patient, and sometimes one an adult one a child. He could say "I met her in an adult chat room and was role playing. I agreed to meet up with the ADULT from the ADULT CHAT ROOM that I met online to roleplay in person." Hard to prosecute that case. Especially if he mentions roleplaying in his chats.
4. The adults are getting on the internet with the sole intent of trying to convince an adult to commit a crime. That is entrapment to the letter.
But that being said, you're an idiot if you agree to meet with a "child" for anything nowadays. You can't trust anyone.