Background. Health information systems are inadequate in many countries. For childhood diarrhoea and pneumonia specifically, the leading infectious causes of child mortality worldwide, current data collection methods are not providing sufficient information for surveillance. The collection of health data could be greatly assisted with the use of mobile devices (mHealth). Mobile phone text messaging is widely used, but its potential for health data collection has not yet been realised. Aim. To explore the application of mHealth-based collection of information relevant to childhood diarrhoea and pneumonia in rural China. Methods. A mixed methods approach was used: (i) a survey and semi-structured interviews to assess the usage of mobile phones by caregivers of young children; (ii) cognitive interviews, usability testing and a cluster randomised cross-over study to determine the validity of a text messaging survey on care-seeking for childhood diarrhoea and pneumonia; and (iii) researchers' observations and structured interviews with participants of the cross-over study to evaluate factors influencing participation in mHealth-based studies. Results. Many of the 1854 survey participants (1620; 87.4%) used mobile phones. Of 1014 participants in the cross-over study, 662 (65.3%) responded to the first text message. Of 651 participants willing to participate, 356 (54.7%) completed the text messaging survey. Overall, text message data were moderately to substantially equivalent to face-to-face data. The text messaging survey was acceptable to parents, but grandparents were often unable to use text messages. Among many factors influencing participation were trust, perceived usefulness and ease of use. Conclusions. Text messaging can be applied to collect data on care-seeking for childhood diarrhoea and pneumonia in rural China, but several questions remain, including how to improve accuracy and response rates. Further work needs to advance innovative mHealth-based data collection methods that can improve health surveillance, enhance implementation of appropriate interventions and ultimately save children's lives.