I did a little web research on holiday music for elementary concert bands, and found the following websites as great sources for finding holiday music for your after school band:
The closest thing I could find to a “caroling book arranged for band” was the Christmas Carols arranged by Mark Feezell (Band/Orchestra, with opt. chorus, flexible arrangements), vol. 1 found here:
The American School Music Institute is a website exclusively for elementary school band music. They even have a holiday section! See the following link:
Stanton’s Sheet Music Website also has a listening library. If you go to the following link, they also have a holiday and winter section:
I hope I helped, I wish you luck on your musical endeavors!