Maybe I've lost my mind, but I noticed the exact same problem when I was doing all gold. I replayed Level 11 several times on both all gold and all diamonds. Nothing ever even touched the kids, yet Level 11 refused to give 3 gold stars, and now it's doing it with diamonds to me also. I've had all upgrades for some time. Not sure if I'm missing a quick "touch" on the kids during the last wave, or if there is a bug. I first noticed it during all gold though, and thought it was weird. Anyone else running into this?
Very happy that somewhere in this is some of my artwork. Bummed that I am so bad at these kinda games that I'll never get to see which pics of mine they used XD. A HINT button woulda been a great additional feature. I'm still psyched this is finally released though! :D