Set your mode dial to use "A"perture priority.
Set your Auto ISO function to use ISO100 up to ISO6400.
Set your minimum shutter speed to 1/125.
These settings will bump the ISO setting as high as needed to keep the shutter speed fast enough (1/125 or better) to stop motion to a large degree without using any flash. You'll have to experiment to find the smallest aperture you can use that also provides a good depth of field, though. I like shooting around f/8, just as a general rule, but indoors I'd be comfortable going to, say, f/4 or so most likely.
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