This study is the first to examine the experiences of children aged 9–17 who have a military or emergency first responder (EFR) parent with post-traumatic stress disorder (PTSD). These experiences of children are important to understand through a lens of intergenerational trauma theory, given the high rates of PTSD in these service populations. Additionally, we need to know if they differ from the experiences of children of civilian parents with PTSD. To examine this, we conducted a total of 17 in-depth interviews in Australia with 5 service parents, 5 co-parents and 7 children aged 9–17 who have a parent who had formerly served in the military or an emergency service. Interviewees were not always from the same family. The families included single-parent, dual-parent, separated, and same-sex families. Gender and service type (military or EFR) were evenly distributed among interviewees. We used a critical humanist approach and undertook a reflexive thematic analysis of the interview data. The major themes were (1) parental emotional extremes, volatility, and unpredictability, (2) changes in home and family relations, (3) impacts on child wellbeing, and (4) PTSD awareness and help-seeking. We found evidence of specific impacts for children related to a combination of parental PTSD symptoms and service conditioning and culture. This study highlights the role of reduced parental capacity in the transmission of trauma from parent to child. It provides an evidence base to direct policy and research into targeted and culturally specific therapeutic interventions and support services for children and parents in service families living with PTSD.