Hi Cindy! Welcome back to the old gang! I took the liberty of moving your post into a new thread, so it kind of looks like you made your own new topic. I won't tell anyone that you didn't. ;)
To answer your first question, there is a oval button that you click to make a new topic, it is just below the forum name, on the left side of the page. This button is also at the bottom of the page also on the left side.
In regards to your boy and horse there are a number of interpretations that can be made on it. I can hear everyone groaning now because they think I am going to write a book on each possibility. Well, I might. ;)
In short, if the contest is for prestige only, then you are probably pretty safe. It won't be published, there isn't any commercial gain, it was a public show, and it is a shot of a participant. If all of that is true, I think you would be fine to use it. If there is prize money which could be seen as commercial gain, I still think you would be safe. You aren't selling the image and it doesn't sound like it will be published all over the place.
In long, it was a public show, and he was knowingly participating (or since it was a child, "being allowed to participate"), and it is assumed that photography will be happening. So when some one is taking part in an event like this and doesn't protest on the spot about photography, there is an implied release to photograph the participants. This is similar to being at a park and taking photos of people jogging or walking their dogs, or at the beach doing the same. Being in public most the time gives the photographer an implied release to use those photographs. However, this doesn't neccessarily mean you should exploit the image for all it's worth, as there are some catches. Even when in public, people have expectations of privacy and you are always better off getting a release. This is most important if you capture some one in a compromising position, but some people just don't like their image being used no matter how good the shot may be. Even if you were in the right photographing them, they can cause a lot of headache for you if they aren't happy about it.
Is the boy recognizable in the shot? I am guessing he is, but if he isn't such as if it is a shot from behind him and you can't see his face, then you should be fine. Having an unrecognizable person in a shot goes a long way to not needing a release. If you can't tell who it is, then technically their persona / image or their privacy aren't being invaded. In the case of not recognizable, you are still best off getting a release, but are also pretty safe to use the image for any use without repercussions.
I think the biggest catch for your shot is that he is a minor (and assuming he is recognizable), and it could be argued that his parents weren't aware that photoraphy was taking place. So while you are probably safe, I would highly recommend not using it for any real commercial purposes without a signed model release. But as a portfolio image you are fine, and I think for a contest such as you described you are fine. But I would not use it for anything commercial, nor in a contest where it will be published or circulated in numerous places.
Another way you can look at it is from a newsworthy standpoint. Photographs taken in public or of an event open to the public which have value as being of public interest don't require a release from those in the photo. Of course, there are catches with this one too. The first is that this type of implied release typically only extends to actual news usage, so it would need to be used in a newspaper, magazine, etc. Another is that it would help if you actually were shooting for a newspaper, or did some photojournalism in general, though the basic definition does not state that you have to be a professional, it just helps with your own credibility. This is how the paparazi and other spot news photographers get away with taking photos of celebrities in public, or of a car crash victim on a stretcher, etc.
See, I didn't type thaaaaaaaaat much. Ok, it's a lot. ;)
Hopefully Joe can add some thoughts to confirm or add warning to this. He has more experience with event and photojournalism photography than I do. Most of my experience comes from commercial and stock photography, which is usually done for hire either with releases for the models or an all inclusive "company wide" release by the client.
And if you actually made it this far, a bonus! Here is a link to a PDF that has information about your rights as a photographer and photographing in public. It isn't all inclusive or go into any great depth, it is mostly an overview, but is still usefull info. I recommend printing it and keeping a copy in your camera bag and car in case some one bothers you.