Literary puzzler for Scooby-Doo fans

There exists a book series, published before Scooby-Doo, that features:

• Two girls,
• Two boys,
• A dog with a voracious appetite,
• Villains that often fake supernatural goings-on to scare people off, and
• Traps that the kids use to defeat the villains.

What is that series?

– Kristin

“Jeepers, Kristin, we don’t know! I’d better get reading.”