In the last decade, researchers have reported the erosion of Traditional Medicinal Plant Knowledge (TMPK), including declines in the knowledge about which plant species are medicines and in the practical skills for using these species. Among the various drivers explaining TMPK loss, the processes governing knowledge acquisition and transmission are not clearly understood. In this study we explore whether grandparent-grandchild proximity relates to child's knowledge, namely through oblique knowledge transmission. Based on the assumption that elders are a repository of TMPK, we hypothesized that children's physical and affective proximity to their grandparents might favor the transmission of TMPK and, therefore, be associated to higher child's TMPK. We test this hypothesis using data from children attending two schools in intermediate-rural towns Guadalix de la Sierra and Figueres, Spain. Contrary to our expectations, neither physical nor affective proximity to grandparents was significantly related to children's TMPK. We provide methodological (i.e., omitted variable bias) and theoretical (i.e., intergenerational knowledge transmission is weak or null in the study area) arguments that might explain our results. We conclude by highlighting the need to create initiatives for intergenerational dialogue that foster traditional knowledge transmission.