The tracking on the K-3 is fine for what you want.
Part of a 23 shot sequence (full buffer) of my dog moving at 25 -35 Mph with every frame in focus, shots were selected based on the pose, taking advantage of the increased frame rate to give me twice as much selection.
Contrary to what you might see posted by various knuckleheads on the fourm, you don't need a K-1 to track your kid.
Every thing a K-3 was good at before the K-1 came out, it's still good at.
I'm not sure where all the pictures are demonstrating what you can do with a K-1 you can't do with a K-3 but someone should point me there. I sure would like to see even one sequence demonstrating K-1 superiority. After giving up half the frame rate, it should be downright super.
I've seen nothing from a K-1 remotely close to some of the series I have.
Sometimes, people don't care if the K-1 is better. They only care about if the K-3 does what they want.. Honestly, dudes, the answer to every camera question on the forum, is not K-1, K-1 , K-1, even if it's the only answer some of us seem capable of delivering.
Pentax does make other cameras for other people and other needs. I simply fail to understand the lack of importance some place on frame rate in action sequences. People pay thousands of extra dollars for a few extra FPS. Pentax itself market the K-1 as a field camera, i.e. landscape etc.