Addition and subtraction anchor charts to help the kids remember which way to go on the number line. For even more visual support, place arrows above or below a number line in the direction of subtraction or addition.
Laminate a number ladder, cut small slits in top & bottom & add a pipe-cleaner with a small bead. Use the bead to slide up & down as you complete addition & subtraction problems (",). could do the same thing with a horizontal number line.