Books in Rats of NIMH series

When Margaret and her younger brother, Artie, get lost in the woods on a family camping trip, they are rescued by rats -- the superintelligent rats of NIMH. Taken into the rat's community, the children are safe for the time being. But winter is coming. Margaret and Artie have to get back home. And when they do, they must protect the rats who have helped them. Everything depends on their silence... but it's hard to evade questions forever. Children's Choices for 1991 (IRA/CBC)VOYA's Best Science Fiction, Fantasy, and Horror 1990Parenting Honorable Mention, Reading Magic Award