Touch targets should be at least 48 x 48 dp.
Use TouchDelegate to extend the touchable area of a child view beyond the child's bounds. This an alternative to padding.
http://developer.android.com/training/gestures/viewgroup.html#delegate
This solution updates as the parent layout changes: http://stackoverflow.com/questions/1343222/is-there-an-example-of-how-to-use-a-touchdelegate-in-android-to-increase-the-siz