Background & Objective: Screen time has now become a most concerned issue around the world due its negative effects on children' health. COVID-19 was declared as a pandemic by World Health Organization (WHO) during March 2022 and lockdown was one of the strategy to control disease transmission. This study aims to investigate whether this lockdown caused an increase in screen time and what are its effects on physical, emotional, and behavioral functioning of children. Methods: It was a cross-sectional study including a sample of 260 mothers of children aged 5–13 years from Karachi, Lahore and Islamabad, during March to June 2021. A google survey form was developed and participants were invited using a google link on social media, parents' groups, Whats app groups and school facebook pages. Screen time was measured in number of screen hours per day. Physical health was evaluated through body mass index (BMI) reports. Children's Emotional Adjustment Scale (CEAS) and Strengths & Difficulties Questionnaire (SDQ) were used for behavioral and emotional problems. Coefficient of correlation and t-test was used for examining the difference of means. Results: About 244 (94%) mothers reported that screen time of their children is significantly increased during COVID-19 lockdown. There was a negative relationship observed between screen time with temper and anxiety control (r= -0.13; p= 0.04). However, a positive relationship was found for hyperactivity (r= 0.74; p<0.001) and conduct problems (r= 0.18; p= 0.003). We found a gender difference for screen time (t= 4.39; p=0.001) and hyperactivity (t= 2.35; p= 0.02), where boys were more hyperactive than girls. No significant difference was obsereved for BMI and pro-social behavior. Conclusion: Screen time among children is considerably increased during lockdown and this is associated with low temper control, anxiety, hyperactivity, and conduct problems. Remedial strategies are required at national level; media and school authorities can play a vital role in this regard.