The large omnidirectional child (LODC) anthropomorphic test device (ATD) thorax has a flexible thoracic spine to address chin‐to‐chest contacts in existing child ATDs. To compare this 10 year old‐sized ATD response to human spine data, a biofidelity target was derived by scaling and normalizing adult postmortem human subject (PMHS) thoracic spine dynamic responses to a characteristic 10 year old human response. LODC thoracic spine biofidelity was then evaluated in the same experimental configurations as in previously conducted adult PMHS tests (Isolated Segment Manipulation (ISM), 3.8 and 5.0 m/s frontal sled with vertebral fixation). The LODC demonstrated a thoracic spine response and head kinematic characteristics that approximated scaled human data. The effective stiffness of the LODC in the ISM condition displayed a similar ratio with respect to the adult stiffness as the stiffness scale factor using a published scaling technique. The LODC spine is stiffer than estimated large child human spine response targets and displayed a bi‐modal response characteristic that differed from the uni‐modal human response shape. This behavior was attributed to low cervicothoracic rotational stiffness given very little cervical (neck) flexion. The LODC response was repeatable until spine degradation was discovered near the end of the 5.0 m/s sled series. While the LODC thoracic spine requires more refinement to more closely approximate human response, it shows promise as an enhancement to existing rigid ATD spine designs.