The last one is interesting except for a few things...
1. Where the brick wall dissappears off on the left... it's a bit distracting. I would clone it so it goes all the way or crop it.
2. I would have positioned him so the brick wall wasn't right dead center in his head. Would add some extra interest to the composition and I find the line to his head a little alarming.
3. Your kid's head is dead-center. You want your boy taking up more of the frame, and his head not in the middle of the pic. Better composition. You can fix this to some degree in post by simply cropping out more of the top. (which will cause you to crop more of the sides, of course, to keep aspect ratio)
4. When shooting kids, don't stand over them. Get down on your knees and get at eye level with them. Makes a better composition.
5. The hood up on his jacket makes his head dissapear into the darkness. This isn't necessarily bad, but it reads as a little sinister to me. Think of it this way, if he wasn't smiling, he would probably look like he was up to no good.
6. All these points aside... the brick wall... the hoodie...
a lot of elements of this shot come across as "look! a gang member!" to me. Now granded, I live in the sticks and always have, so it might just be my reaction. There are elements that disspell it... like the big warm smile... but I think you want to try to innocent-it-up a little more. Take his hood down at the very least. Crouch as I suggested. I think it will take most of it away.
If you do it again, try a number of different angles and compositions and look at each and analyze the results.
BTW, don't take offense at my picking it apart. I ONLY do this when the shot is interesting and I think there's something that you can do to make it great. If I thought it were utter garbage you would never hear from me.
(I agree with everything Derrel said, btw)