I have the Canon 6D. It is a good camera, but....but not for action. Once in awhile is fine, but regularly shooting kids running around.....save your $ and get a refurb 5D3, an 80D, a 7D2 or the A6500.

I also have a Sony A6000. The AF system has a hard time tracking dogs running at the park, so I expect it would have a problem with kids too. However the AF system is updated in the A6500 and have read it is much better. However battery life is an issue.

I would rent the 80D, 7D2, 5D3 and the A6500 w/ adapter and see which fits your needs better.