Just some ideas-try a "sit wherever you want"day. They (and you) will have a totally different listening environment. You will hear all kinds of things that you hadn't heard before.
Set them up in a circle with you in the middle. Again, you will all hear things you hadn't heard before.
Both of those are fun for the kids and it might get a few more days worth of work out of them.
They need to be mature to do this one, BUT.... have them go through various sections of the tunes playing only when they have the melody. An individual might rest 2 bars, plays 3 beats and rest another two bars. Or the entire section might play 8 measures, but it gets the kids aware of who has the melody and when. It also forces them to concentrated focus.
Doing the OPPOSITE helps as well. No melody, only play if you are the background voices. When they switch from melody to accompaniment, they need to be aware of their volume and how they fit in to THAT balance of sound.
Have percussion play throughout both of those.

Hope this helps!