Journal of Clinical Sleep Medicine is dedicated to advancing the science of clinical sleep medicine. In order to provide subscribers with access to new scientific developments as early as possible, accepted papers are posted prior to their final publication in an issue. These papers are posted as received-without copyediting or formatting by the publisher. In some instances, substantial changes are made during the copyediting and formatting processes; therefore, the final version of the paper may differ significantly from this version. Unless indicated otherwise, all papers are copyright of the American Academy of Sleep Medicine. No paper in whole or in part may be used in any form without written permission from the American Academy of Sleep Medicine.

It is still debated whether lockdown conditions in response to the coronavirus disease 2019 (COVID-19) health crisis seriously affected children’s sleep. For young children, some studies identified more insomnia, while others only transient disturbances, or even no effect. Based on the premise of mother–child synchrony, a well-known dynamic established in child development research, we hypothesized that principally, the children whose mothers perceived the lockdown as stressful and/or responded maladaptively, suffered sleep disturbances. The main objective of this study was to identify the family profiles, variables, and lockdown responses most linked to insomnia in young children. The sample consisted of 165 mothers, French vs. Swiss origin (accounting for different lockdown severities), of children 6 months to 5 years old. Validated sleep, stress, and behavior scales were used. Multiple regression, age-matched clustering, and structural equation modeling analyses provided evidence that insomnia in young children is indeed strongly linked to the mother’s reaction to the pandemic and lockdown. Specifically, reactions such as COVID-19 fear/anxiety and obsessive COVID-19 information seeking coincide with heightened vigilance, cascading into reduced child social contact, outings, and increased screen viewing, ultimately culminating in child insomnia and behavioral problems. Mother education level and child day care quality (e.g., home-schooling) were also identified as strong insomnia predictors.