* Mother tongue refers to the language a child first learns to speak and understand, usually from their parents or caregivers. It's the language they are most fluent in and feel most comfortable using.
* First language refers to the language a person learns first, regardless of who they learned it from. This can also be the mother tongue, but it could also be a different language if, for instance, they were raised in a bilingual household.
In most cases, a child's mother tongue and first language are the same. However, it's important to note that in some situations, there may be a slight difference:
* Adoption: A child adopted by a family speaking a different language than their biological parents might have their mother tongue as the language they were exposed to before adoption, and their first language as the language of their adoptive family.
* Bilingual families: A child raised in a bilingual home may learn both languages simultaneously. In such cases, it might be difficult to say definitively which language is their "first" language, as both could be considered equally important.
Overall, "mother tongue" and "first language" are often used interchangeably, and they generally refer to the same thing: the language a child learns first and is most fluent in.