First off, parents should be warned that both the complete and "highlights only" editions of the RENT soundtrack are explicit and are for ages 15+ only. That said, the innapropriate content is isolated in select songs, and some of the numbers are kid-friendly. I wouldn't recommend any songs besides "Seasons of Love" and "Finale B" for anyone under the age of 12, but most of the songs are good for ages 13+. Secondly, parents should know that in the movie and recording, lots of songs (even harmless G-rated fare like "I'll Cover You") are sung by homosexual couples, thus, the implication of something racy is always present, even when explicit content is not. Almost all of the songs besides the three mentioned above contain mild profanities ("d**n" and "h**l") and considerable, though pretty vague, innuendo (look up individual song lyrics for details). Two songs on the CD ("Tango Maureen" and "La Vie Boheme") are explicit and not for anyone under 15. The first song contains two "f" words and is about a character who cheats with both men and women. The latter song may/may not contain another "f" word (depending on what version you listen to) and numerous references to mature things like AIDS, homosexuality, homelessness, S&M, marijuana, and anarchy.
This is really good music that contains iffy stuff, but also promotes friendship and loyalty. As a rule, though, keep the majority of songs for when your kids can understand and appreciate them.