Persistent Insufficient Sleep from Toddlerhood to Early Childhood: A Longitudinal Actigraphy Study

Background/Objectives: Sleep in early childhood is essential for healthy development, yet insufficient sleep remains highly prevalent. This study aimed to characterize longitudinal changes in objectively measured sleep patterns, to compare actigraphy-derived sleep measures with parental reports, and to identify predictors of insufficient sleep. Methods: In this longitudinal cohort study, healthy children were assessed at 18–29 months (T1) and 30–41 months (T2). Sleep was objectively measured using wrist actigraphy over 72 h, while parent-reported sleep habits were collected through structured questionnaires. Agreement between actigraphy-derived sleep parameters and parental reports obtained through the Sleep Habits Questionnaire (SHQ) was evaluated using intraclass correlation coefficients (ICCs) and Bland–Altman analyses. Logistic regression models were used to examine whether insufficient sleep at T1 predicted insufficient sleep at T2. Associations between behavioral factors and sleep outcomes were assessed using generalized linear models with repeated measures. Results: A total of 185 children were assessed at T1 and 176 at T2. Mean ± SD total sleep time (TST) remained stable between assessments (10:07 ± 63 min vs. 10:10 ± 62 min), although both bedtime and wake-up time occurred later at T2 (p = 0.003 and p = 0.005, respectively). Children with insufficient sleep at T1 had increased odds of insufficient sleep at T2 (adjusted OR = 3.21; 95% CI: 1.40–7.37; p = 0.006). Moderate agreement between parental reports and actigraphy was observed for bedtime and wake-up time, whereas agreement for TST was poor, since parents consistently overestimated TST and underestimated nocturnal sleep fragmentation (p < 0.001). Nighttime milk intake was associated with lower sleep efficiency and more awakenings, while exposure to blue light before bedtime was associated with shorter TST and higher sleep latency. Conclusions: Insufficient sleep persisted over time. Nighttime feeding and blue light exposure were associated with less favorable sleep outcomes. Early identification of at-risk children and objective sleep assessment may support targeted interventions.