I'm not so sure that he should be prosecuted at all. The equivalence to this is breaking into someone's house.. by asking their two year old if they can go inside and for the key.
If you asked a two year old if you can come in and did, you would/could be prosecuted. For trespassing amongst other crimes. Two year olds do not have legal capacity to consent. Technically you could be prosecuted if a 15 year old let you in - although you probably wouldn't be. It depends on the parents. And it depends on what you did - specifically did you commit an additional crime while there.
Reading someones private email is a crime, as is posting it, as is trying to mess with an election.
If you told the kid a lie in order to get in you could also be prosecuted for fraud.
It's an equivalent level of security.