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US lesbian couple's son pens book on what makes a family

30 August 2012 Last updated at 03:04 BST

At age 19, Zach Wahls became a YouTube sensation when he delivered a passionate speech on the floor of the Iowa House of Representatives in favour of same-sex marriage.

Three years later, he wrote a memoir about his life, his parents and the importance of marriage and family.

In his book My Two Moms: Lessons of Love, Strength, and What Makes a Family, Wahls argues that his life is not much different from most Americans, and discusses the pain of being painted as a threat to "traditional values". He says that family - no matter how it's constructed - is a fundamental building block of society.

In doing so, he hopes to deliver a message to other kids with same-sex parents who feel outcast: you are not alone.

The BBC spent a morning with the Wahls in Iowa City to find out what family means to them.

Produced for the BBC by Leigh Paterson.