How old are the kids?
Next, kids often need a WIND-down time, before nap, to key down. They can't do this AT nap time... so BEFORE actual nap time... start winding them down already... make everything quiet... turn off things, make the room dark etc. Read stories to them, while they get into their spots.
You have to do something, CALM and QUIET... BEFORE actual nap time... to key them down.
Personally, I would NOT have a "play time" after lunch... because it will just get them too hyper, before nap. For me, if my kids horse-play before nap or sleep... they CANNOT sleep. Even if tired.
So, after lunch time for your group of kids.... have a wind-down time, and transition them into something QUIET... like read to them. And also cue them, verbally.... ie: "After lunch, we get ready for nap....and wind-down..." Then, do it. Emphasize, "TEAM work".... when doing so.... use that word.... also say "This is our routine..."
In their nap room... have NOTHING in there to play with. Just their sleep mats etc. And make that room DARK. Take out anything stimulating...
Really, do NOT have a 'play-time' after lunch... and before nap, have them use the bathroom or change their diapers etc. Make that a routine too. For my son, he 'cannot' nap, if he has to poop, for example. Which he does, after a meal.
For me, it takes me about 1/2 hour to 1 hour to Wind-down my kids BEFORE actual nap time. So, I get them ready for nap... BEFORE the actual nap time. Make sense? Otherwise, getting them ready and wound-down, eats into the actual nap time.
Its all about PREPPING them, BEFORE actual nap time... and getting them to key down.
good luck,
Susan