Q: how i can connect ipad with ipad mini via bluetooth

for what purpos?

this is what bluetooth profiles ios devices support out of the box

http://support.apple.com/kb/HT3647?viewlocale=en_US&locale=en_US

but there maybe more features supported by apps from app store as a bluetooth profiles such as PAN give the client server possiblities

What are you trying to do?

Bluetooth peer to peer connections between iPads are supported by certain Apps like Photo Transfer, gaming, etc. See here: http://support.apple.com/kb/HT3621

There are no other ways to pair iPads via Bluetooth.