I've never gotten a child out of focus with the 6D.
Never? I can only conclude that 1) you don't shoot many kids, or 2) you are hyperbolizing to the point where it becomes a lie. No AF system is perfect, they all miss, it's just a question of frequency. Sorry, I don't buy 'never', except in that way that I can honestly say I've never gotten a Sasquatch or a Yeti out of focus.
Yes, I own the 6D. You do not. Apparently you have not even tried one. The difference between you and me is, I have tried (besides the previous cameras I've owned) a 7D, a 5D3, a 5D2, a 1DX, a 1D4, and a 1Ds3...besides some Nikons. My judgment is not clouded. Yours is, besides being ignorant of the 6D, having not tried or compared one for yourself.
If it helps you to believe that, that's fine by me. However, it's not true. In fact, a few weeks ago I was at a kids' birthday party, at which several of the parents had dSLRs and we had a nice round robin with a 1D X, 5DIII, 6D, and 7D (I opted out of trying the 7D, since I own one). In my case, I tried them with the 70-200 II and 85L II. There were static (briefly) kids, running kids, jumping and sliding kids (it was a 'bouncy house' thing), all in pretty crappy lighting (>ISO 3200 to have a hope of an action-stopping shutter speed).
All three bodies did great with static kids and one shot center point AF. With the peripheral points and the 85L, the 6D often (>20%) failed to lock or locked after excessive hunting, whereas the 5DIII and 1D X had no problems (thus, I can see what the poster who called it a '1-point system' means). With the peripheral points and the 70-200 II, the 6D did as well as the others on static subjects.
With servo and moving kids, the 6D did ok, but just ok, with the 70-200 II, and not well at all with the 85L. The 5DIII and 1D X were hard to distinguish (I could see the active points stick on the faces with the 1D X, whereas the 5DIII often went to shirts, etc., but at f/2.8 and the distances involved, the DoF was sufficient). Kids running diagonally toward me gave the 6D the most trouble - a higher miss rate for that than I found acceptable. When I tried servo tracking with an outer point on the 6D, it would frequently start out in focus then drift successively to backfocusing as the kid ran closer. The 1D X and 5DIII had no problem in that scenario. That may be technique, though - I suspect if I'd used just the center point, the 6D would have fared better. But that would mean cropping away a lot of the final images, since for composition purposes I prefer to leave the subject 'room to run' within the frame. With the center point on the 6D, the handoff to the outer points sometimes 'missed' and the outer point would lock onto a pipe on the wall or something - the high density of the 5DIII/1D X AF sensor makes those handoffs seamless.
But it really doesn't matter. What matters is that you're happy with your 6D and it gets you the shots you need. While my experience with the 6D was limited, I owned a 5DII for years. While I really liked the IQ, I was frequently frustrated by the limitations of the AF system with moving subjects. My brief experience with the 6D left me with the conclusion that while it was definitely improved compared to the 5DII, I would still be frustrated with it.