1- Great picture as is, but I'd love to see a closer zoom on the kids or a slight crop to remove some dead space over their heads. I like the use of the foreground grass, but there is only blade going over the boys face that I find distracting. Could just be personal taste though.
Nice sharpness and colours too.
2- The expression looks a bit forced. The best kid portraits are kids acting natural. Watch that overhead sun as its hitting his hat making the top part blown out (too white). Nice DOF. Again, I'm not liking the centered face in the frame.
3- Lovely capture! This is a Hallmark moment

. Great sharpness and DOF. I like how the light hits the back of her head, lighting her hair. I love how the tire is out of the frame, but would of loved to see that little part of the foot that is missing still in the frame.
But really, thats just me. I love the picture though.
4- Not really liking this one. Technically its nice, but again, the subject is too centered in the image, there is alot of dead space over her head. You did a great job with backgrounds in the other 3, but this one has a busier background, specially that bush or whatever in the back right over her head.
You have alot of the technical parts of photography down...exposure, shutters and what not. Nice job all around. Keep working on the focus though
Work on that composition though. Look into the rule of thirds, fill the frame with your subject and watch that dead space over their heads.
You can also post up bigger pictures
Looking forward to seeing more of your work!