Well this has already been answered but I'll chime in anyway -
One of my first photography challenges was getting good pics during indoor school events, sans flash.
I learned quickly that 1/60 is the right shutter speed for all but the most hectic movement - I was taking photos of chorus and violin performances.
So if photography is, mechanically speaking, a balance of ISO, shutter speed, and aperture, you want lenses of f/2.8 or faster to have a high shutter and low ISO.
With your zoom lens at f/5.6 (rather than 2.8) you lose "two stops of light", so to keep the same shutter speed you have to go from 400 ISO to 1600.
At first I was using a zoom lens indoors and didn't understand the mechanics of photography, so rather than the needed 1/60 I was two stops off getting motion-blurred kids at 1/15
So two stops matters
The good news is, for Pentax users, our cameras can use the old manual focus lenses that have fast apertures of 2.8 and beyond.
135mm f/2.8 and 50mm f/1.8 and 28mm f/2.8 all work fantastic in tough situations like photographing indoor school events without flash.
Also know that depth in focus* increases with distance - for example, f/2.8 might not have much depth in focus at a distance of 4 feet - but taking photos o the stage that is 100 feet away will give it much more depth in focus. You can use this calculator to see :
Online Depth of Field Calculator
So with a 135mm lens at f/2.8 and the subject at only 4 feet, the depth in focus is slim at 0.03 feet, but at 100 feet away it becomes an amazing 19 feet. So don't be concerned about a shallow depth in focus.
(*technically called "depth of field", it means the amount of depth in focus)
So, just like others have found - use a fast aperture lens, set your shutter speed appropriately, and use "auto ISO" - you'll be all set
It's a lesson I learned the hard way
Have fun!
Craig