You can also do something they've seen, but in a new way. Read it backwards. Read from bottom to top (line 1 measure 1, line 2 measure 1, line 3 measure 1 etc). Top to bottom. Diagonal. Go down the row - first person play measure 1, next person measure 2, etc without stopping.
Once you've got rhythms down on a unison note, play scales in those rhythms. Up and back down on a Bb scale. When they get to the top and run out of notes, they turn around and come back down. Use whatever keys you want. It makes them think.
Most sight-reading problems are rhythm problems. If the kids can read the rhythms, they'll usually get the notes. If they don't, a wrong note is a lot less obvious than a wrong rhythm.