Development of asthma in children may be associated with exposure to particulate matter (PM). However, stationary samplers may not represent the personal exposure of children aged 3 and younger since they may not detect particles resuspended from the floor as children play. To address this issue, an autonomous robot, the Pretoddler Inhalable Particulate Environmental Robotic (PIPER) sampler, was developed to simulate the movements of children as they play on the floor. PIPER and a stationary sampler simultaneously measured particle number concentration in six size channels (03-10 pm) using an optical particle counter in 65 homes in New Jersey, USA. For all investigated particle sizes, higher particle resuspension was observed by PIPER compared to the stationary sampler. In 71% of carpeted homes a more significant (at the alpha = 0.05 level) resuspension of particles larger than 2.5 mu m was observed by PIPER compared to the stationary sampler. Particles larger than 2.5 mu m were resuspended more efficiently than smaller particles, over both carpeted and bare floors. This demonstrates that PIPER is able to resuspend particles through movement, and provide a better characterization of the resuspended particles than stationary samplers. Accurate measurement of resuspended PM will improve estimates of children's exposure to PM. (C) 2015 Elsevier Ltd. All rights reserved.