Background and objective Over the past few decades, new infectious diseases have emerged,and these have played a key role in changing behavior and lifestyle in all age groups. More recently, with the emergence of the coronavirus disease 2019 (COVID-19) pandemic, governments around the world have made unprecedented efforts to contain the epidemic by implementing quarantine measures, social distancing, and isolating infected individuals. Social behavioral adaptations (e.g., social distancing, isolation, etc.) impact children's and adolescents' lifestyle activities and lead to increased incidence of psychosocial problems, worsening of preexisting mental illness, and fears of infection, uncertainty, isolation, and stress. In light of this, this study aimed to assess the impact of COVID-19 on the behaviors and lifestyles of the children and adolescent population of Pakistan. Methodology A cross-sectional study was conducted involving 323 children and adolescents bytargeting parents of children and adolescents in the age group of 4-18 yearsliving in Pakistan.The study was conducted from April 2021 to September 2021. A well-designed structured questionnaire was used to collect data about the sociodemographic profile, attitudes, and behavioral factors impacted by COVID-19 in children and adolescents. SPSS Statistics version 23 (IBM, Armonk, NY)was used to enter and analyze data. Results Parents or caregivers of a total of 189 male and 134 female childrenaged between four and 18 years took part in this study.During COVID-19, the consumption of fast food and fried foods by children and adolescentsincreased significantly.In this study, out of 323 participants, almost all (289, 89.5%) had increased their screen time significantly.Nearly half of the total individuals experienced the feeling of depression and loneliness during the pandemic. Additionally, some children and adolescents felt fearful when leaving home. COVID-19 lockdowns have led to many changes in children's and adolescents' lifestyle habits. They reduced physical contact with others due to the fear of transmission of COVID-19. Based on our findings, the pandemic and its containment strategies have adversely affected the behaviors, lifestyles, and attitudes of children and adolescents. Conclusion Governments around the world have imposed social distancing during the COVID-19 pandemic, leading to adverse short-term and long-term negative mental health issues such as unhappiness, fear, worry, irritability, depressive symptoms, anxiety, and post-traumatic stress disorder (PTSD). Interventions are needed to focus on building resilience in children and adolescents, addressing their fears and concerns through better communication, encouraging routine and physical activity, and taking measures to alleviate loneliness.