In this paper, a wearable sensor system embedded in a belt for monitoring cardio-respiratory activity in children with neurodevelopmental disorder is presented. The sensors are integrated, using a micro-controller with a wireless interface, in a network that is able to transmit the monitored parameters to a data collection station. The data are acquired, processed and stored using a virtual instrument developed in the LabVIEW environment. The aim of the study is to evaluate the effectiveness of cardio-respiratory frequency, observed in structured and non0-structured situations of interactive session, as a possible indicator of stress response in children affected by autism spectrum disorder and by pre-school language disorders. Preliminary results evidence a correlation between specifically designed activities and the corresponding heart rate.