You know, that happens alot in Ultraman as well. Some kid sees a monster, tells someone aboout it and they don't believe him. Even though the city suffers from monster attacks and alien invasions on a regular basis!
I reckon the scenario should play out like this:
Kid: "officer! I just saw a monster!"
Cop: " oh crap. what type of monster was it? Is it Godzilla? Or Baragon? We're not being invaded by mushroom people again, are we?"
Kid: "um... no. It had more than one head...I think."
Cop: " WHAT? It's Ghidorah? Quick! Alert the science Patrol! or G Force! Break out the Maser cannons! Raunch the lockets!"
Ahem. Sorry about that. Got a bit carried away there...
But if it played out like that, there'd be no story, would there?