mp3 rocket does the exact same thing as limewire and bearshare. Its just another client for downloading songs files from gnutella. Trust me on this, if you download songs, movies, apps from gnutella using ANY client youre going to be running the risk of infringing copyright. If your sons want to download music and you want to be sure youre doing it 100% legally, use itunes or eircom and the like. 99c per song or whatever it is now. Yes, some bands do put out free mp3s, but none in the Uk Top 40 that I know of.
Also on gnutella, even with adult search filter off, its nearly impossible to search for anything without getting returns of "debbie likes big <insert desired appendage>.mpg". know what i mean?
Gnutella does have its uses tho (check out Direct IP link on limewire for transferring files online from pc to another) so if youre determined to at least try it, Id suggest limewire as the client for its features.