Wow that sounds like the school where I tutor! There are some good books with African American and Hispanic illustrations, do you want them all in English or would Spanish work as well? The school where I tutor/sub is English only, so that limits some of what they take… anyway, oft the top of my head -
Esperanza Rising
Abuela
Too Many Tamales
Josefina (American Girl)
Cactus Soup
Free Baseball
Going Home
You might look for authors Tomie DePaolo, Eve Bunting, and Christopher Paul Curtis. Also Jerry Pinkney is an AA artist/illustrator.
Also - see whether the school is registered with First Book - they have GREAT books at extremely discount prices.