You might try to get some of the better adults involved in the teaching. Give them some picture books and tell them to practice reading it at home. Then have them come back and lead reading time or something.
I think if you empower them as teachers, they'll get more from the class, but then if you do too good of a job, you'll soon be missing some students
Basically, I try to teach those classes to the kids but teach the parents what they need to continue the lesson at home and grow with it. Teaching them to read books to their kids is one of the biggest areas I focus on.