There's no motion blur, it's a toddler going slower than his normal walking speed shot at 1/800, the consensus earlier was that a slower shutter speed was good for a toddler running, which is faster than this. I obviously had the luxury of being there, and I can tell you his head was down the whole time, it's not motion blur.
I'm sorry but I really doubt you're correct here, I've shot enough table tennis using a 200mm f/2.0 near MFD to have seen this exact issue time and time again. I know somebody said something about 1/640s being enough but in this case the shutter speed simply isn't fast enough to get a pin sharp image due to the lens being shot wide open at a fairly close range. Now why am I so sure of this? It's not because I'm being a big ole' internet meanie intent on insulting you. Let start with some things we can, hopefully, agree on:
- There exists a point on the ground that is very sharp.
- The ground is stationary.
- The front wheel is out of focus.
- The rear wheels are out of focus.
- The region of sharp focus is located somewhere between the front wheel and the rear wheels.
So, if we can agree on these and we suppose that shutter speed is fast enough for motion to not be an issue then you should be able to locate some point on the subject that is just as sharp as what we see on the ground. If it is front focus like you're thinking then somewhere on the fork, head tube, or steerer tube should be sharp. To my eyes there's nothing on the entire subject (child and bicycle) that is as sharp as what we see on the ground, but I'm interested to hear what you see in the image.
Not great contrast granted, but I was aiming at his face not his forehead, with 5 or 9 points selected covering his entire face, and it is showing a focus point so focus was 'achieved', allegedly.
The second one is very likely a failure of the AF system to some degree, generally if you get an entire sequence OOF like that then the camera had trouble locking onto some high contrast target at the beginning and just flubs through the entire sequence.