ipad app automatically startup

you mean like a login item on the computer? no, there is no way to do that - as far as I know...

 

Have a look under keyword "guided access"

http://www.macrumors.com/2012/09/19/ios-6-feature-guided-access-also-for-kids-and-kiosks/

I didn't tried myself but that might goes in the direction what you want

You find it in settings under accessibility

 

Sure, just as a suggestion for be next question please specify your environment more detailed (what generation of hardware and software versions). It will allow a better help.

When iOS6 is not an option I have no other idea.