My Literal Child

My kids are preparing to sing a song with the children's choir for our church's Easter musical.  We have a conflict with the actual choir practice time, so they are to learn the song on their own, and they will attend the rehearsals when or if they can.  Today, I played the song for the first time, "Sing Hosanna".  My kids liked the upbeat song, but when it was over my eldest said, "Mom?  Who is Hosanna and why are we telling him to sing?"