Background A number of studies have reported that depression is associated with lower relative left frontal activity in the alpha band (i.e. frontal asymmetry, or FA), as measured by electroencephalogram. FA has also been hypothesized to be a vulnerability marker for depression. If this is the case, FA should be evident in offspring of depressed mothers, a group at elevated risk for depression. However, the results of previous offspring studies have been inconsistent and none of these studies has considered whether the relationship between FA and risk changes over development in children. Method We assessed FA twice, at ages 3 and 6, in 253 never depressed children from a community sample. Maternal history of depressive disorders was determined by a diagnostic interview completed by the mothers at the first assessment. Results There was a significant interaction between maternal depression and offspring age at assessment, indicating that FA exhibits different developmental trajectories depending on level of familial risk for depression. Offspring of depressed mothers exhibited a decreasing relative left FA over the course of early childhood, while offspring of nondepressed mothers exhibited relatively similar, symmetrical, levels of frontal alpha activity at both assessment points. Conclusions These results suggest that changes in FA from early to middle childhood distinguish those at risk for depression and that cross‐sectional assessment of FA may have limited value in understanding risk. These results highlight the importance of considering development in understanding the role of FA in depression.