Generally at conventions, pregens are provided. Sometimes the description will make that clear but not always. Most DMs do not allow players to bring characters because they can tailor pregens to the adventure and do not have to worry about someone with an overpowered character or magic item. If the DM wants (or will allow) players to bring their own, they will mention it. Sometimes they may have other notes for players, such as Jim Ward, who will say something like, "Bring a list of 10 normal items you would like your character to have." If there is something like that listed, you want to make sure you follow the instructions and are ready to go when you sit at the table.
The huge exception to the pregens is if you are playing an official organized play campaign where you are expected to keep playing the same character in multiple games. The examples of this at Gamehole this year are the Pathfinder Society games and the D&D 5e Adventurers League games, which is what you are playing, correct? There should be pregens provided for the games for characters of 1-4 levels. If you wish to bring your own character for a 1-4 level game, that is fine. Just make sure it is a legal character, as there are specific rules required for creating characters for the Adventurers League. If you are playing a higher level game, you will be required to bring your own character that has advanced through playing the lower level adventures.
You can go to http://dndadventurersleague.org
to download the Players Guide for the current season so you can create a character to bring with you if you wish.
If the game description says younger players welcome, then the game is open to players of all ages. There are a few games that will specify that they are a kids only game, but younger players welcome just signifies that the game doesn't have content that would be inappropriate for younger players and that the DM is fine with children playing. Some may not wish to have younger players in their games.