Have 5 iOS devices, certain games don't install on 1 iPod

I have the following iOS devices:

2 iPhone 5

1 iPhone 4

2 iPod 4th gen (front/back camera)

There have been a number of times that I'll get a game on 1 device (usually my iPhone 5), and the other devices are setup to automatically download new apps. The problem is that one iPod 4th gen, my daughters, will not install a few games -- namely temple run, temple run 2, and subway surfers. The other devices all download/install these games just fine. It's my daughters ipod that is the only problem. In the app store on her ipod, the "Free" (download button) is greyed out and not clickable. Other games have the download button appear just fine (Temple run Brave shows up, for instance).

The odd thing is that her ipod will download some apps just fine, but not those two games (and there are others, I just can't remember them).

I've updated all devices to 6.1, and each has plenty of storage available.

I don't have any clues as to why it won't download these games/apps. Is this a hardware problem? Any ideas?