Many mental disorders begin in early childhood. Without timely treatment, mental disorders experienced by young children can impair their learning ability and relationships with others, causing lifelong complications. However, not all children with a mental disorder in early childhood receive treatment. Using data collected from 46,424 children aged 2 to 8 years in the 2 most recent cycles of the National Survey of Children's Health (2021 and 2022), we estimated the prevalence of having a mental disorder and investigated factors associated with young children not receiving mental health care when needed. All analyses were adjusted for survey weights to account for the complex sampling design and nonresponse biases in generating nationally representative estimates. In 2021 and 2022, 19.0% of US children aged 2 to 8 years had 1 or more mental disorders. Of these children, 9.1% reported not receiving any needed health care in the previous 12 months, and of these, 45.8% reported not receiving mental health services when needed. The primary reasons for not receiving needed health care were problems getting an appointment (72.1%), issues related to cost (39.3%), and services needed not being available in the area (38.5%). Poor experiences with health care providers were consistently associated with not receiving needed mental health services among children with mental disorders. Our findings suggest a strong link between health care factors and not receiving needed mental health services among US children with a mental disorder in early childhood. In addition to increasing the availability of mental health services and expanding health insurance coverage, future public health efforts should prioritize enhancing patients' experiences with health care providers.