Parents influence offspring aggression through genetic and non-genetic mechanisms, although the latter are less well understood. To examine potential non-genetic effects of parents on offspring, we cross-fostered the highly aggressive and biparental California mouse (Peromyscus californicus) and the less aggressive, less parental white-footed mouse (Peromyscus leucopus). In-fostered animals within each species were used as controls. We examined associations between the foster parents’ behavior and aggression of the fostered male offspring in resident–intruder (R–I) and neutral arena aggression tests. When both species and fostering groups were combined, R–I aggression of offspring was positively associated with paternal time spent retrieving pups. In contrast, aggression in a neutral arena was negatively associated with a composite score of maternal behavior. We discuss how our findings regarding paternal retrievals may explain previously reported effects of cross-fostering on male aggression.