I found the sentence
バスから降りた、制服に身を包んだ少年少女たちは全員この門をくぐり抜けていく。
translated as:
All the boys and girls in uniform got off the bus and passed through the gate.
What would be the difference with some equivalent expressions like: 身につける、or others ? Does 身を包んだ add some kind of nuance ?
I don't see any deeper nuance to the phrase 身を包む. It literally means 'to wrap yourself up', or in other words 'to wear'. To me, it simply conveys that they were dressed in uniforms. You don't mention the source but I am assuming it is from a novel perhaps? As with English, writers often use alternative ways to express something if they feel it is too prosaic. If that were the case here, instead of using 制服を着ている少年少女たち which is perhaps a little prosaic, the writer might have wanted to choose a more 'literary' phrase like 制服に身を包んだ.
I found the question
日本語の用法に関する質問です。 服を着ることを包むと表現しますか？
and the following answer
まず「身を包む」という言い回しがあります。 「スーツで身を包む／スーツに身を包まれた」という表現がよく使われています。 それが省略されて「スーツに包まれた」という表現も比較的よく使われているようです。 ただし、これは「着飾る」という意味で使われます。 単に服を着るだけでなく、おしゃれをし、盛装しているということで 場の雰囲気を考慮した装いをしていることを示しています。
which translates roughly as
The phrase "スーツに身を包む" is often used. It seems that the expression abbreviated "スーツに包まれた" is also used relatively often. This is used to mean "dress up." Not only wearing clothes, but also dressing up in fine clothes, they are dressed in consideration of the atmosphere of the place.
So to sum up, it means "well dressed" alhough it would be often translated as "to wear"
source: https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1283150307
