Argument from personal incredulity: because you cannot understand why they made themselves known to those children, it therefore must not have happened.
Argument from even more total incredulity, to believe that Aliens would travel the distance that they would obviously needed to have travelled, and the time involved, and the obvious advanced Intelligence they would have, to "appear" to a group of children, with a warning "mind meld" message, that we are ruining our planet, instead of at the White house, Buckingham Palace, or the Kremlin with their message.
Oh, I did forget, you also accept Bigfoot, ghosts and goblins on similar "hear say" evidence.
Extraordinary claims, require extraordinary evidence.
Gullible people that believe the "total incredulity" that Aliens would travel these distances, to appear to isolated individuals or groups, to deliver a planet saving message, then again disappear to probably appear to another isolated individual, to conduct some anal probing or similar, without leaving any credible evidence of their visitation, is to accept the tooth fairy, Santa Clause and the Easter Bunny also.
Yep, our gullible impressionable children saw a UFO...100% certain.
The rest is 100% unknown.