When photos began circulating of migrant children separated from their parents and placed in what looked like giant cages in detention centers, the young adult novelists Melissa de la Cruz and Margaret Stohl had an immediate response. After texting nine author friends asking what they could collectively do, Ms. de la Cruz and Ms. Stohl drafted a statement of protest called “Kidlit Says No Kids in Cages,” denouncing “practices that should be restricted to the pages of dystopian novels.”

Within minutes, they had 94 signatures from “our fellow kidlit authors and supporters,” Ms. de la Cruz said. A day later the statement was posted on Twitter with over 4,000 signatures. The group has now raised nearly $240,000 for legal services for the migrant families.

They also expanded fund-raising to include online raffles and auctions for such services as manuscript evaluations by best-selling children’s authors and “character naming,” with the winning donor’s name to appear in an as-yet-to-be-written novel. Another group of kidlit authors, agents and publishers made an online clearinghouse of original posters designed by prominent children’s book illustrators to protest family separation, all available for free download.

Children’s book creators similarly coordinated a response after the Marjory Stoneman Douglas High School shootings in Parkland, Fla., in January. The graphic novelist Raina Telgemeier and the YA novelist Jenny Han set up a group called Kidlit Marches for Kids, rallying colleagues to join the March 24 gun control protest spearheaded by the Parkland students, and designing a protest sign for marchers.