Mother tongue?

Three mothers.
One father.
Five different languages.

For three generations in our family
three mothers and one father have
been teaching a mother tongue to their
own child - a mother tongue that is NOT
their own mother tongue.

Which means that children's rhymes,
children's songs you grew up with, are
in most cases not passed on to your child.
At least not to the extent it would have been
natural if there was only one language and that
was the father's or mother's mother tongue.

On the other hand, you as a parent had to
learn your child's "mother tongue" and learn
the child culture in that language in
a conscious effort, as a grownup.

Mother tongue - for whom?