Background: With technological advancements, smartphone usage has increased significantly among children and adolescents. While these devices offer educational benefits, concerns exist regarding excessive use and its impact on health, behavior, and social interactions. The COVID-19 pandemic further accelerated smartphone dependency due to online education. Objective: To assess the patterns of smartphone usage among children and adolescents and its impact on sleep, eating habits, academic performance, and behavioral outcomes. Methods: This prospective cross-sectional study was conducted in the Department of Paediatrics, Maharishi Markandeshwar Medical College and Hospital, Kumarhatti, Solan, over 18 months. A total of 300 children aged ≤18 years attending the paediatric OPD or admitted to the paediatric ward were enrolled. Data were collected through parent/child interviews and analyzed using SPSS version 21.0, with a p-value <0.05 considered statistically significant. Results: Smartphone usage was universal (100%), with a mean starting age of 1.81 ± 0.78 years. During the COVID-19 lockdown, daily screen time increased significantly (p = 0.0001). 45.6% of parents reported sleep disturbances, 80% noticed changes in eating habits, and 21.3% observed a preference for smartphones over outdoor play. 18% of children were perceived as addicted, while 14.7% experienced visual problems. Conclusion: Smartphone usage is widespread among children, with increased screen time affecting sleep, diet, and physical activity. While educational use is beneficial, parental regulation is minimal, increasing risks of overuse. Strategies promoting balanced screen time and digital well-being are essential for mitigating adverse effects.