The continuity, co-occurrence, and co-development of child internalizing and externalizing problems have been extensively studied and considered to be causally related either directly (directional model) or indirectly through an underlying shared or related liability factor (common vulnerability model). This study used child self-report to avoid rater bias in determining the continuity and cross-development of child internalizing and externalizing problems over a 1-year period, examining both direct pathway and indirect pathway by using maternal mental health as underlying explanatory mechanism. The Dominic Interactive, a computerized child self-report instrument, was used to assess internalizing and externalizing problems in 178 primary school children, aged 6-11 years old, over a 1-year time interval. Their mothers reported on their own maternal mental health at baseline. A cross-lagged path model was tested using Structural Equation Modeling. The results confirmed the stability of child-reported internalizing and externalizing problems but showed no cross-developmental paths. Maternal mental health at baseline was related to child externalizing behavior 1 year later. The theoretical explanations involve the developmental timing of the cross-developmental paths and the strong co-occurrence of internalizing and externalizing problems at both time-points. This study showed the value of the Dominic Interactive as a child self-report instrument in addition to other informant measures in assessing child mental health problems over longer periods, especially when maternal mental health is involved. Furthermore, deprived maternal mental health warrants clinical attention to prevent externalizing problems in primary school children.