Youth in foster care are more likely than their peers to require mental health supports to promote their well-being, and this level of need has likely been heightened by individual, familial, system-level, and societal factors arising during the COVID-19 pandemic. These changes have simultaneously produced a shortage in the supply of available community-based providers; a lack of available beds in emergency, inpatient, and residential mental health settings; and staggering delays in the provision of necessary services once such youths' needs are brought to the attention of relevant professionals. As a result, youth have increasingly experienced treatment and placement delays that have resulted in lengthy psychiatric boarding episodes and improper placements in hotels and child welfare offices. This study employed community-based system dynamics and group model-building methods to understand the complex factors and processes that have contributed to treatment access barriers and placement delays for this population. Results suggest that increases in the prevalence of complex mental health needs among children, insufficient preventative and screening resources, low capacity and quality in psychiatric residential treatment facilities, workforce shortages, and ineffective assessment and referral processes exacerbate treatment delays and negatively affect child well-being. The system maps created in this study highlight the need to implement multipronged approaches that concurrently address system capacity and quality issues while also improving pathways to care for children with complex needs.