They won't play games unless they are overweight.That's why they won't play unless you feed snacks.You can also try feeding them regular meals to get their weight up.They'll eat a couple extra meals even if their hunger meter is full.
Also NEVER stuff them with snacks.One or two is fine,but don't feed them more than three or four at a time max and that's only if you want to get their weiht up for some reason.If you give them a bunch one after another they will get sick.