Anne-Cath Vestly (1920-2008) was a Norwegian author and radio broadcaster of children's programmes, where lots of her books first appeared. Most of her characters end up in her fictional town of Trilltoppen and a key theme of her work was inclusion and representation of different family structures, doing this (at least to my knowledge) in an incidental but clearly planned way.
Her series include:
Ole Alexander - Where a working class city boy goes to live in the country.
Grandma and the Eight Kids - Features a large, intergenerational family.
Little Brother and Knerton - A family with both parents working and the challenges that can bring.
Aurora - Children brought up by a father who stays at home while the mother is out at work.
Guro - A child brought up by a single mother.
Kaos and Bjørnar - Themes of disability and world peace.
Ellen Andrea - Brings back lots of characters from earlier series and particularly focusses on international solidarity and immigration.
Sadly, the vast majority of these book have not been translated into English so these descriptions are not based on my own reading of the books. I would love to get more translated so if you have any knowledge of how to do this please get in touch on twitter.