A former “punk” illustrator and a refugee’s daughter have performed an American double, taking two of the UK’s most prestigious children’s literary awards. Lane Smith’s There Is a Tribe of Kids won the 2017 Kate Greenaway medal for illustration and Ruta Sepetys’ Salt to the Sea received the Carnegie medal for best children’s writing.

Chair of judges Tricia Adams described the winning books as demonstrating “the vitally important role that literature and illustration play in helping children and young people to understand the world around them, be that through a historical lens or through the natural world around them”.

Salt to the Sea is a fictionalised account of the sinking of German ocean liner the Wilhelm Gustloff in 1945. It was the worst maritime disaster in history, in which 9,000 passengers, mainly refugees, were drowned. As the daughter of a Lithuanian refugee, the story of the had particular resonance for Sepetys. Her father’s cousin was meant to sail on the ship, but on the day of the voyage was unable to board. “She suggested that I write about the sinking and the refugees from many different countries evacuating through East Prussia,” Sepetys said.

Describing herself as thrilled by the award, she added: “When I interviewed people during my research, some told me not to bother with the book, that the world had forgotten them. The interest in the novel confirms that through characters and story, historical statistics become human and suddenly we care for those we’ve never met.

“My work sits on the shoulders of nonfiction, memoir and testimony. If a reader is interested in my novels, it’s my hope that they will feel compelled to research the facts behind the fiction.”

Of Salt to the Sea, the judges said that “not one of us knew about this real-life disaster and it shows how history is skewed towards the victor”. They added: “[The book] has been selected because of the powerful, crafted language, the tight, carefully shaped plot and the range of moods evoked throughout.”

The Wilhelm Gustloff liner leaving Tilbury Docks, circa 1938. Photograph: Hulton Getty

Smith’s There Is a Tribe of Kids won the Kate Greenaway medal for illustration because “of the warm and playful images, which show how children are influenced and inspired by the world around them”, the judges said. Blending unusual collective nouns with images from nature, the book explores the emotional range of a child as she searches for a new home.

The Connecticut-based illustrator said winning a UK award was especially significant to him, since his earliest influences had been British illustrators. “When I was starting out in the early 80s, it was a more conservative time in [US] illustration, but fortunately after a while, people were able to slap a label on my work as ‘new wave’ or ‘punk’,” the 57-year old said.

He admitted he had to forgo his punk influences for the award-winning book, choosing to ignore the darker collective nouns available. “There were some I would love to have used, like a ‘murder of crows’, and 30 years ago I would have done that, but now I think that is a little bit harsh for children,” he said.

The two books emerged from shortlists dominated by stories of displaced and refugee children. Two other books were chosen from each of the eight-strong shortlists to receive Amnesty Cilip honours for children’s literature exploring human rights: The Bone Sparrow, a novel by Australian author Zana Fraillon about an unlikely friendship struck up between a refugee child and a local boy; and The Journey, illustrated and written by Italian artist Francesca Sanna, which follows a family of refugees.

The medals, which are overseen by the Chartered Institute of Library and Information Professionals (Cilip), became mired in controversy earlier this year after the 20-book longlist for the Carnegie featured no BAME (black, Asian and minority ethnic) writers, despite their very strong showing on bestseller lists and other prize lists, including the Costa and Guardian children’s book prizes.

As a result of outcry headed by authors including Alex Wheatle and Philip Pullman, Cilip announced an inquiry into equality and diversity in the information sector and the Carnegie award, which has never been won by a BAME writer in the 80 years it has been run.

Accepting the 2017 Carnegie prize, Sepetys welcomed the inquiry. “What a meaningful way to commemorate an important anniversary, with a commitment to inclusivity, diversity, and to address issues that divide our societies,” she said.

She added: “We must constantly challenge ourselves to do better, to be gentle with one another, and be willing to look through another’s eyes and consider their heart.”