A repertoire is not built overnight, and for most players, having a deep theoretical knowledge is not required. They simply need to understand opening pawn structures.
That said, if this child is showing a great deal of aptitude, it may be worth adding this to your study regime earlier than I would normally recommend. I have seen two prodigies up close, and ...
1939: White to Play and Win by Weaver Adams. Adams believed that 1.P-K4 (1.e4) wins by force. In this book he presents his recommendations for White against the various Black defenses. For example, against 1...e5 he recommended the Bishop's Opening 2.Bc4. He continued to revise his system and write more books, e.g., he switched from 2.Bc4 to 2.Nc3 in his ...
The reality is that you cannot force such openings as black, but you can pick openings that may suit your style.
I really think that the Nimzo-Indian/Queens-Indian may suit your style very well. They will not get you queenless positions too often right out of the opening, but the nature of the Nc3 in the Nimzo, and it often getting exchanged resulting in ...
I know what type of positions he enjoys playing, so opening will be easy to select.
In that case the hardest part is already behind you. Let me suggest the following strategy: Copy the repertoire of a grandmaster.
Pick a high-level player would style you think would fit you pupil. The correct pick should be a principled player, who uses regularly the same ...
In 1561 Ruy Lopez (pronounced Rue-y Lopeth) de Segura (1530-1580) wrote Libro de la invencion liberal y arte del juego del Axedrez, por Ruy-Lopez de Sigura, clerigo, vezino dela villa Cafra. He wrote the book in response to Damiano's book. It contains 66 games. In 1584, his book was translated into Italian by Gio. Dominico Tarsia and printed at Venice by ...
"How to Think Ahead In Chess" by I.A. Horowitz and Fred Reinfeld was published in 1951. For white it covers the Stonewall attack. For black its the Sicilian dragon and the Lasker variation of the Queens gambit declined. An odd combination of openings.
In the Grandmaster Repertoire series, there are three books covering the English opening from white's perspective, written by GM Marin in 2009 and 2010: Volume 1, Volume 2 and Volume 3.
More recently, in 2016, IM Cummings wrote a repertoire book based on e3 systems, rather than fianchettoing the bishop with g3.
Update: In 2018, a new repertoire series from ...
For many years the standard work on the English was the four volume series written by John L Watson - "English I: ...P-K4", "English II: ...N-KB3", "English III: ...P-QB4", "English I: ...Other Lines". Written in descriptive notation and republished a few years ago by Harding Simpole.
This might be the first one: "Opening Repertoire for the Attacking Player" by David Levy and GM Raymond Keene. It was first published in 1976.
Here is another in a similar format: "The Chess Opening for You: A Complete System for White and Black". It was first published in 1975.
It is well worth reading Mikhail Shereshevsky's advice for trainers building a chess repertoire for their pupils.
I am afraid this quite a long quote, but this section can be found online free of charge here(pdf), and I encourage readers who want to learn more to purchase Shereshevsky's book or e-book,
The Shereshevsky Method to Improve in Chess.
Despite there already being some great answers, let me emphasize a few things: Take into consideration that we are not trying to build a repertoire from scratch. Your student probably knows already a few things about certain openings. Use that knowledge and expand on it.
You should find a repertoire that powers his strenghts and is comfortable to play for ...
I recall reading My System by Nimzovich. That must have predated the 1970ish books noted. Assuming repertoire means what it seems to mean otherwise PCO would have been earlier than 1970ish.
It would appear to have been a series of booklets later put into the form of a single book circa 1930s.
I still suspect there were earlier books from Italy and ...
Practical Chess Openings had openings in the 50s & 60s like Modern Chess Openings had later, and others have now.
I suspect there were some opening books that go back a lot further but they would have been more limited.
I also recall a few, not many, books that specialised in a given opening.
I would personally stick to learning a few e4 and d4 variations and maybe the English Opening, though I didn't see it much at lower level play. I am also adding some fun, fairly solid variations if you wanted try the more obscure openings
1. e4 e5
2. Nf3 Nc6
A personal favorite of mine, especially the Rio Gambit Accepted line 1.e4 e5 2.Nf3 ...