I like candid snaps, so number 2 and 4 I like..
Number 1;
The similarity in colour between the hair and the sand at the background is a little too close for my liking. The fact that the shore was at the hairline is unfortunate and highlights the similarity, but other than that no probs..
Number 3;
Could be the angle, or the hard shadows under the eyes and chin but I don't find this to very flattering at all, in all honestly I think it makes the youngin look quite sickly. I did a little lightening work, just using the Lighten/Darken brush in Paint Shop Pro to show you what I mean..
3 points ( 5 really ) Under each eye, under the chin a little, and a small amount on the eye itself.
Also, speaking as someone with a large head.. I would have maybe come from a different angle as I think that's a lot of forehead in the front of the shot.
You asked for a critique.. hope I haven't offended..