Do your primary children's EYES sometimes wonder when they should be looking at you? 
I know mine do. 
I make the motion for them to stand up, and only about half will stand up while the others are off in lala land ;) 

So here's a fun idea to help them watch you. 
Hold up "All eyes on me" sign before you are about to stand to sing.  Every time you do this, wear a new pair of glasses.
Hopefully it will help!!!! crossing fingers..not eyes :)