Well Seduce the Villain's Father is similar, but they haven't had kids yet ;)
You might have already seen it but
"I became the hero's mom" is the closest kind to this, and it's real good!!
http://www.mangago.zone/read-manga/a_stepmother_s_m_rchen/
http://www.mangago.zone/read-manga/i_raised_cinderella_preciously/
http://www.mangago.zone/read-manga/i_became_the_hero_s_mom/
http://www.mangago.zone/read-manga/i_became_the_mother_of_the_strongest_demon_lord_s_10_children_in_another_world/
I swear theres more but my ass cant remember-
can yall recommend me manhwas like this or something that the fl became a mother or what