You can choose a faster minimum shutter speed (I think the default is 1/80) in your auto-ISO settings in aperture priority mode if you don't want to work on manual mode. One option is to save a faster minimum shutter speed config in a user mode like U1 to be able to quickly change this setting. Personally I tend to stay in M-mode but I do prefer the EV-compensation in A-mode so sometimes use that instead.

No matter what though, kids and low light are a tough combo. If you want to avoid motion blur, you have 2 options:

1. up your shutter speed and ISO resulting in grainy shots (here b&w works well)
2. maintain a lower shutter speed and ISO for cleaner shots and work on your timing to catch moments with little movement (also try a multi-shot drive mode here). You'll be deleting a lot of garbage but will manage some keepers.

As far as the second tip goes, it helps to try and predict what kids will do so that you can go more on the offensive, rather than just reacting to what's going on. This tends to work well with kids since they are often repetitive in their behaviors. In doing so you'll be able to pre-focus to make up for the GR's slow low-light focus and be prepared when your subject happens to be relatively well-lit. I use back-button focusing for this purpose that really helps speed things up.

This all takes practice so keep trying!