On 17 August 1839, passage of an Act to Amend the Law Relating to the Custody of Infants. The Act allowed a separated wife to petition the court for custody of her children under the age of seven. The campaign to change the law was led Caroline Norton (pictured). She experienced domestic violence in her own failed marriage. In response, she wrote a pamphlet that discoursed on the natural rights and gifts of mothers. 

Image courtesy of Wikimedia: https://commons.wikimedia.org/wiki/File:Portrait_of_Caroline_Norton.jpg

Sources: http://www.branchcollective.org/?page_id=68

https://www.parliament.uk/about/living-heritage/transformingsociety/priv...