The Significance of Sleep Problems in Early Childhood for the Long-Term Well-Being of FamiliesAbstract: Theoretical background: Clinical sleep problems of infants and toddlers are associated with several negative outcomes for further development, especially if they persist. While a corresponding considerable strain on affected families is well-known, evidence of the potential consequences for longer-term family well-being is sparse. Objective: To examine (1) whether early childhood sleep problems predict family well-being at the parent and parent-child-relationship level as well as the child's negative emotionality 2 years later; and (2) whether prior parental burden due to children's sleep behavior mediates this influence. Method: We used data from a representative longitudinal study of N = 669 families (M-Age parent at T2 = 36.93 years, SD = 4.95; 7.0 % fathers) with young children up to the age of 5 years (M-Age child = 39.62 months, SD = 11.28; 49.5 % girls). At two measurement points, parents reported well-being at the parent (anxiety and depression symptoms via PHQ-4, relationship satisfaction via DAS-4) and the parent-child-relationship level (doubts in parenting competence, bonding difficulties via PSI) as well as markers of child negative emotionality. Additionally, at T1, we assessed symptoms of child sleep onset and nighttime waking problems as well as parental burden due to their children's sleep behavior via parent report. Mediation models tested the statistical impact of sleep problems at T1 on reported indicators of family well-being at T2 via parental burden. Results: The range of sleep problems was large in this sample (M = 1.01, SD = 1.17). The mediation models showed a significant impact of the quantity of T1 child sleep problems on family well-being at the parent level, i. e., symptoms of depression and anxiety, as well as at the parent-child-relationship level at T2, i. e., doubts about parenting competence and bonding difficulties, with complete mediation via T1 parental burden due to as a result of the children's sleep behavior. Discussion and conclusion: Early childhood sleep problems significantly impact well-being at the parent and the parent-child-relationship level even 2 years later. A determining factor mediating the longitudinal association seems to be the corresponding parental burden rather than the infants' and toddlers' symptoms themselves. Impairments of parental well-being and the parent-child relationship should be considered even more in the diagnostics and therapy of children's sleep problems.