Objective: Conventional whole-head MEG systems have fixed sensor arrays designed to accommodate most adult heads. However arrays optimised for adult brain measurements are suboptimal for research with the significantly smaller heads of young children. We wished to measure brain activity in children using a novel whole-head MEG system custom sized to fit the heads of pre-school-aged children. Methods: Auditory evoked fields were measured from seven 4-year-old children in a 64-channel KIT whole-head gradiometer MEG system. Results: The fit of heads in the MEG helmet dewars, defined as the mean of sensor-to-head centre distances, were substantially better for children in the child helmet dewar than in the adult helmet dewar, and were similar to head fits obtained for adults in a conventional adult MEG system. Auditory evoked fields were successfully measured from all seven children and dipole source locations were computed. Conclusions: These results demonstrate the feasibility of routinely measuring neuromagnetic brain function in healthy, awake pre-school-aged children. Significance: The advent of child-sized whole-head MEG systems opens new opportunities for the study of cognitive brain development in young children.