This page includes two versions of the alto saxophone music for What Child Is This? One is a solo version in a slightly easier key of B minor (concert D), and one is in the key of F sharp minor (concert A) which allows you to play with other band instruments. Visit the What Child Is This? lead sheet page which features the carol in seven different keys. There you can find your desired instrumental range, or print an arrangement that allows you to play along with string instruments or the recorder.
See the transposition page for explanations and charts to help you determine the appropriate key to play in when performing with instruments that are not in concert key. More Christmas songs for alto saxophone.
What Child Is This? version for alto saxophone and other wind and brass instruments: