Background Research on the psychological experiences of parents of infants within pediatric oncology is sparse. This study examined rates and indicative risk factors for psychological distress in parents where there is either an infant patient or infant sibling of a patient. Methods Participants were mothers (n = 41) and fathers (n = 25) of infants under 2 years who either had a cancer diagnosis (n = 37; infant patients) or was an infant sibling of an older child with cancer (n = 29; infant siblings) recruited from a single oncology center. There were 21 couple dyads. Parents completed the Depression Anxiety Stress Scales short form and the Posttraumatic Stress Disorder Checklist. Results Mothers (47.5%) and fathers (37.5%) reported elevated, cancer‐related posttraumatic stress symptoms. Rates of depression (12.2% of mothers and 12.0% of fathers) and anxiety symptoms (17.1% of mothers and 8.0% of fathers) were lower. Compared with parents of infant patients, parents of infant siblings reported significantly higher rates of depressive symptoms and trends toward higher rates of posttraumatic stress symptoms and anxiety symptoms. Parent anxiety was higher with increased time post diagnosis. No demographic or illness‐related variables were associated with psychological distress, with the exception of the number of children in the family. Conclusions Parent–child relationships are of fundamental importance during infancy. This study provides novel data highlighting the psychological impact for parents when a cancer diagnosis is made during this critical developmental period, including the contribution of family structure to parental distress. Results provide further support for applying a traumatic stress framework when exploring parent experiences of pediatric cancer. Copyright © 2016 John Wiley & Sons, Ltd.