When the early nesting dolls were
created, all of them were presented with females as their biggest dolls. That
is because a couple of the main symbols of the matryoshka dolls were of
depicting a woman’s fertility and their motherhood. The shape of the
big-bellied doll almost portrayed a mother’s stout figure and her significance
in the family by the nesting of her “children” dolls inside.

Mothers play a big role in the traditional Russian family;
being the bearer of life and her capability to multiply her seeds are just some
of them. In the country, having a big family is considered as a common practice
and even an important one; there are usually more than three children, as well
as members of the extended family live under one roof with them. Each member of
the family is believed to have their own unique role in the household, and it’s
the mother who serves as the foundation of the home. (Source)