my IPad mini will not recognise my bluetooth headphones my other IPad recognised straight off

If you want a chance at a definitive answer then some questions:

What make, model, and version headphones do you have? What level BT do they use 2.1, 4.0?

What is your "normal" iPad? iPad 1, iPad 2, iPad 3, iPad 4?

What iOS level is your "normal" iPad running?

You say, "My normal IPad 2 third gen."

Does that mean that you have an iPad 2 or an iPad 3?

The iPad 2 running iOS 6.1.3 will use BT 2.1 while the iPad Mini running iOS 6.1.3 will use BT 4.0.

Although BT 2.1 is upward compatible with BT 4 some BT 2.1 drivers don't implement the 2.1 standard correctly and there can be pairing and other problems trying to use them with a BT 4 implementation.

This might be the cause of your problem. Check with whomever the headset manufacturer is to see if they have a solution.