A majority of children with mental health problems do not access mental healthcare. This study examines factors that facilitate access to mental healthcare services and prescription medication when children's mental health deteriorates, focusing on the mother's economic resources and her perceived assessment of her child's emotional problems. Using longitudinal survey data linked to national medical records, we find that the child's self-assessment of emotional problems, rather than the mother's assessment, most strongly predicts future self-harm and suicidal behaviours. However, the mother's assessment more strongly influences whether a child accesses mental healthcare as their emotional health declines. The mother's educational attainment and the child's age and gender, also influence mental healthcare access. We identify factors associated with greater congruence between the child's and mother's assessments of emotional problems, suggesting areas that programs could target to improve children's access to mental healthcare.