OK, how do you prove that the person on the other end who's planned to meet them is, in fact, an adult, unless they arrange a meeting and they turn up? At that stage, the intent has turned into them commiting a crime.

You can't convict on a suspicion, you can use your suspicion to be ready to catch someone in the early stages of a crime and prevent them going further, but you can't convict on a suspicion.

I could joke and say, "I'd really like to steal all of the Queen's money." Somebody quite literal may take that seriously and suspect me of plotting to steal her money, they couldn't convict me of that though.