Labour attacked the Conservatives' child tax credit proposal through an advertisement on the main forum page. The Tories reportedly plan to respond through a video on the site.
The community website, set up by mothers to give advice on parenting and family issues, has turned into a platform for major political parties to woo female voters.
Politicians now view Mumsnet users as "political animals" who are engaged in the election and keen on understanding the issues that affect their lives.
Mumsnet's co-founder Justine Roberts has stated that the site's managers had pondered "long and hard" before allowing political advertisements.