The accepted phrase is mother tongue because of the association of learning your language from your mother/father. Native is usually associated with land and country

There is no difference - they mean the same thing. Both are the language you grew up speaking; the one you speak 'perfectly'. In English you can also call it your 'first language'. My native language/mother tongue/first language is English.

yep, mother tongue is the language which a person has grown up speaking from early childhood ^__^ this is the usual word-combination and another meaning of mother tongue is any ancient language (like Indoeuropean) to which ur language has genetic relation