The delivery of an aerosolized drug to a child is a complex process requiring an interaction between parent, child, and inhalation device. Recent studies have shown that the facemask can be a key factor affecting aerosol delivery, particularly the influence of leaks between the facemask and the face. To further quantify these effects and design around them, we have developed a bench model consisting of a breathing simulator, an inhaled mass filter, and a "pediatric face." This paper reviews the development of this model and details important decisions made in its configuration, particularly inhaled mass filter location (e.g., between device and facemask, or in mouth) and mouth diameter (4 or 18 mm). With the final design, we used the model to measure the impact of the "blow-by" technique on nebulizer inhaled mass. In a separate series of experiments, we studied the effects of a "crying" pediatric breathing pattern on inhaled mass for both nebulizers and pressurized metered dose inhalers with valved holding chambers (pMDI VHCs). Results indicated that the location of the inhaled mass filter was a critical factor in assessing aerosol delivery through facemasks and that the "mouth diameter" was not an important variable. Failure to locate the filter in the mouth behind the face, especially for jet nebulizers, failed to accurately measure effects of the facemask and significantly overestimated aerosol delivery. Blow-by results indicated that a 1-cm gap between the facemask and the face was not critical when using a front-loaded facemask. Finally, even with optimal design, the combination of an aerosol generator and facemask with a crying breathing pattern reduced the inhaled mass to 1% of the label dose.