Airplay
TThe icon is missing on only itouch, ipd2, iphone4. It is available on my iPhone 6 and 6 plus. Ive made all the ios on each device as current as possible and validated they are compatible with my apple tv. How do I fix it?
Apple TV
Here are the hardware requirements for Airplay:
Use AirPlay to wirelessly stream content from your iPhone, iPad, or iPod touch - Apple Support