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Yes, if you transferred music from your iTunes Library to your son's computer, you would be able to delete the music from your library. Before doing so, or any time you make a lot of changes to your iTunes library, I would suggest creating a backup.
Home Sharing your iTunes libraries among your family computers
Home Sharing enables you to stream or transfer music, movies, TV shows, apps, and more among up to five authorized computers in your household. To do so, you will need to turn on Home Sharing on each computer using the same Apple ID. Once set up, all the libraries from these computers will show up in the Shared area of iTunes:
With Home Sharing, you can stream music and video from one authorized computer to another, or drag music between computer libraries. You can also choose to have iTunes automatically import purchases you make on any of your Home Sharing computers to your own library. To do so, select the library and use the Settings button at the lower right of the iTunes window to select what you'd like copied.