Budget around 400: My son wants a camera for free running (running, jumping, climbing, summersaults etc quick movements, requiring fast tracking, possibly in low light levels). He wants this as much for movies as pictures.
He was advised to get a Canon 700D but to me the spec, especially for movies wasn't as good as for the other models mentioned.

I've currently purchased the DMC-G5, as has less shutter lag and does 20 fps continuous shooting. I'm now having second thoughts as the spec for the A58 and NX are better in other areas eg pixels, I'm not sure which has best detection for tracking this kind of movement and 4/3rds vs APS-C. The NX is really stretching the budget for the tasks required but do want to consider.

Any advise greatly appreciated, though not too technical please as my knowledge is very limited. My son also has limited knowledge, so camera needs to be user friendly but with options to improve as he learns.