First things first - welcome to TPF. Lots of info to be found here.
1. I love the little guys expression in this shot, but the water fountain cutting him in half isn't good. If it were not for the fountain itself, it could have been a cute shot because it would have shown him just reaching above the bar, but as is the round part of the fountain cuts into his face and becomes a distraction. Also the bar tips to the right a bit and makes the image lean.
2. I would suggest cropping it tighter, cutting off the top of a persons head is acceptable in some cases, in this case just a tad into his hair. I think think this would help because of the tree leaves and blown out sky. Cropping up from the bottom will help by getting rid of the red shirt and collar of the person holding him and the viewers eye will me more quickly drawn to his face.
3. Again I would suggest a tighter crop. Some off the top to get rid of the white glare and in a bit from the right so the viewers eye is drawn more the the man and childs faces and the tender moment.
4. Crop this one down from the top to about midway of the trees in back so the boy isn't competeing for attention with so much blown sky in back.
Its usually a good idea to have your backgrounds be a contrasting color to the persons clothing, but the green shirt against the grass isn't too bad here. Also watch that your backgrounds aren't too busy, so that your main subject, and in this case an adorable one, stays the main point of interest. Over all, not bad for a first attempt.