Abstract Introduction Coronavirus disease 2019 (COVID-19) has affected both physical and mental aspect of people worldwide, especially the high-risk group such as pediatric cancer patients. Children with cancer were considered both clinically and mentally vulnerable during this pandemic. They were also affected by the self-isolation, quarantine, and social distancing policy taken as a respond to public threat. Objectives To evaluate the impact of social distancing and health protocol during COVID-19 on the mental health profile of children with cancer in Indonesia. Methods A cross-sectional study evaluating the mental health of children with cancer during COVID-19 pandemic was conducted in Cipto Mangunkusumo Hospital, Jakarta, Indonesia from June to September 2020. An online questionnaire was used to collect demographics of parents and children, children's Strength and Difficulties Questionnaire (SDQ) score, and parents' Self-Reporting Questionnaire (SRQ). SDQ score consists of five subscales, including the emotional symptoms, conduct problems, hyperactivity, peer relationships problems and prosocial behavior. Cancer types were grouped into retinoblastoma, nonretinoblastoma (other solid tumors), and leukemia. Results There were 156 valid responses, consisting of 42 patients with retinoblastoma, 34 patients with nonretinoblastoma (other solid tumors), and 80 patients with leukemia. Pandemic-related lifestyle changes did not significantly impact emotional or behavioral problems. Children with normal total SDQ (odds ratio [OR]: 473, p = 0.001) and emotional scores (OR: 3.19, p = 0.07) had parents with normal SRQ scores (<6). Leukemia patients with shorter diagnosis period had worse hyperactivity score (p = 0.01). On the contrary, leukemia inpatients had better prosocial scores than outpatients (p = 0.03). More bilateral retinoblastoma patients (p = 0.04) with longer duration of cancer diagnosis (p = 0.03) faced peer problems. Conclusions Our study revealed that lifestyle changes during early COVID-19 pandemic were not major factors impacting emotional and behavioral problems in children with cancer. However, disease-related factors pose great challenges; thus, a holistic mental health support system should be available to both children and parents.