Mini soccer

1.

First off, what's wrong with their faces. They should get that checked out.

Horizons are way off in all of them. Since I don't know what you were shooting or how you were shooting, it makes it tough to comment. I see a lot of blurry feet, so bump up the shutter speed. Also, bump up the ISO a little if you have too. The guy with the watch who is eyeing the kids in #1 is a bit distracting. You could tighten the crop to fix that. Subjects need faces, that being said #3 just doesn't work. If the keeper is the subject of #4, then crop it like he is the subject.

Hi,
for the Italian law we can not publish people images without authorization.

Thanks for the advises, I will correct the photos soon.

With their faces blurred out this way, it will be tough to comment on.

Faster SS and bump the iso.

It is weird having the pixelated faces.

Anyway, regarding advice above , I would not necessarily go for higher shutter speed /bumping ISO. At least not always. In fact most of the time not.

First pic for example, a fraction of a second later and with a slower shutter speed you'll have most of the player sharp but the swinging leg will be blurred
emphasizing motion.

If someone asked for a photo of their son playing I'd use a faster shutter just to ensure I'd get a sharp shot. For my own pics, I'd try for slower shutter in the ope of some motion blur.

Same applies for a golfer swinging , tennis player serving etc

Even someone starting a top fuel dragster:

I crop the first pic but the subject is not properly at focus.