Both were released before PG-13 happened, but in all fairness, I'd argue Gremlins and Indiana Jones and the Temple of Doom (also PG in the US) were responsible for the creation of that rating.

Here in the UK, things were different. Indiana Jones and the Temple of Doom had over a minute cut to get it down to PG (these days it is uncut). Gremlins had a 15 certificate (there was no 12A in those days, our equivalent of PG-13) and Poltergeist has it's own fascinating and bizarre history with the British Board of Film Classification. More about that here, if you're interested. :)

Poltergeist: 40 Years On | Fanfare