There are generally 2 main schools of thought when it comes to choosing openings.
The mainstream school believes that you should start to learn the main lines of theory, accumulate the experience gained over tournament games and then emerge with a better understanding of the game.
The other school's main emphasis is on practicality - to be able to enjoy chess without spending too much time. Hence the main idea is to adopt off-beat gambit lines, learn them well and work on the element of surprise.
In my opinion, both schools have their points and merits. For an interested student of the game wanting to grow into a player of international standing, the mainstream school should be the way to go - however, it does amount to spending lots of time in gatherting the information about the history of the opening line, studying the key ideas from playing over the key games on which theory has evolved, then checking through the current state of theory. In addition, there's also the need to look at deviants of the opening and to be conversant in refuting them as well. Such an approach can only be recommended if you truly make chess your one and only hobby outside of your main activity. No TV, no XBOX, computer games etc. Chess becomes your main entertainment
For students with lesser interest and ambitions, I honestly cannot recommend this approach for reasons of practicality. Our students are often swamped with loads of schoolwork, tests, projects and what not - there's simply not enough time to handle the huge demands of school as well as the chessboard. One needs to work smart in this case. The nice bit about chess is that there's really many ways to skin a cat. Hence the subject of gambits.
Gambit play is often recommended for young players because it introduces the concept of tempo and initiative at an early age. No one can afford to waste any time when playing a gambit because the advantage of time in development is transient and disappears rapidly when your opponent catches up with you in piece development. Then there is the necessity of having good tactical vision in order to make the gambits come alive. Learning tactical ideas coupled with good opening development habits makes learning and playing gambits fun and rewarding as opposed to memorising tomes of information without much understanding.
Please note that I am not advocating the use of gambits in winning miniature games through the traps ingrained in them. Resorting to "tricks" is not the right way to learn chess. However, we cannot deny that these traps are the result of punishing your opponent's indulgant moves in the position. So understanding how the traps are sprung is a necessary step in learning the opening, but it should not be over-emphasised as an end in itself.
A main component of junior chess improvement is the ability to generate threats at every move coupled with precise calculation of the opponent's possibilities to the threats. Playing gambits requires the correct execution of the sequence of threats in order to achieve the right conditions for the attack against the opponent's king or else the attack quickly fizzles. For students 10 years or younger this would work out fine. As the child grows, mainstream openings can then be introduced as he would by then realise that for all gambits, the secret to answering them is not to keep the pawn plus, but to return it at the right time to realise and advantage.He will then be at the right point of his chess development to appreciate the intricacies of the Ruy Lopez, the Sicilian and Queens Gambits or Slav defences which are the staple openings in any World Championship match.