Straight historical manhwa with kids playing the cupid for their parents

https://www.mangago.zone/read-manga/the_count_s_intruders/

It’s more like just one child doing the job (and only to some extent)

https://www.mangago.zone/read-manga/i_failed_to_divorce_my_husband/

This one has like the starting bit that matches your requirements and that too its not around the main couple. the main couple actually are the kids who play cupid

https://www.mangago.zone/read-manga/the_heroine_wants_me_as_her_sister_in_law/
https://www.mangago.zone/read-manga/minence_grise_female_lead_is_trying_to_make_me_her_stepmom/
https://www.mangago.zone/read-manga/i_became_a_sitter_for_the_obsessive_villains/
https://www.mangago.zone/read-manga/i_will_take_responsibility_for_the_welfare_of_the_male_lead/