Hi, Streams after 12th to enroll in are:

• Bachelor of Engineering (B.E or B. Tech)- Information Technology (IT)
• BCA
• BSC IT

You can also enroll for a degree in computer science, software engineering, or another programming related field and specialize in mobile application coding.

Very importantly, as a mobile app developer, you will be working in at least one of the five major platforms  Android, iOS, Windows, Symbian, or RIM (Blackberry). While you can and should be able to code in all these platforms, you will have to choose one to specialize in when you are just starting out.
BUT this is for later stage.
Hope this helps.
Good Luck.