I had the same problem and started using a one-on-one fly drill. Have your WR run a fly, get your DEF to backpeddle until the WR is close (but before they are to you) then turn and run with the WR. I also teach getting a hand on the WR (minor contact not called in our league) so that you know where they are and can turn your head to the QB. As far as picking up from one zone area to the next, constantly preaching communication on DEF... use of short words like "Steve Help" or "Bill coming Right" really help. The other thing we do is have pre-set zone converages-releases. This eliminates the kids from having to think to much and lets them play more. For example we run a 3-1-1, our RLB is one of our faster players, so that player always has a deep coverage while the safety stays to the middle/left side. The MLB then covers Middle/Right.... switching the 3-1-1 to a 2-1-2. This has worked well and the kids are never confused as to who was supposed to go deep and who wasn't. Hope that helps!