This article explores analogy as a communicative tool used by parents to relate children's past experiences to unfamiliar concepts. Two studies explored how similarity comparisons and relational analogies were used in parent-child conversations about science topics. In Study 1, 98 family groups including 4- to 9-year-olds explored two science museum exhibits. Parents suggested comparisons and overtly mapped analogical relations. In Study 2, 48 parents helped first- and third-grade children understand a homework-like question about infections. Parents suggested relational analogies and overtly mapped analogical relations for children. Use of relational analogies was positively associated with scores on a post-task measure of understanding. These studies suggest that parents help children learn about unfamiliar science topics by suggesting personally relevant or culturally pervasive analogies and by elaborating unfamiliar and non-obvious analogical relations. (Contains 1 figure and 1 table.)