Background: Coronavirus disease 2019 (COVID-19) has upended societies and dramatically altered everyday life across the globe. COVID-19 is a highly contagious viral illness caused by severe acute respiratory syndrome. Aim of the study: To assess the effect of preventive nursing guidelines about COVID-19 on hospitalized school age. children Research design: A quasi-experimental research design was used to carry out the study. Setting: The study was conducted in pediatric medical department at Benha University Hospital, which consists of three wards.  Sample: A purposive sample of hospitalized school age children (75) child admitted the above-mentioned setting for treatment during the period of data collection (six months) were included in the study. Tools of data collection: Two tools were used. Tool (I): A structured interview questionnaire sheet to assess personal characteristics of hospitalized school age children, and their knowledge related to COVID-19. Tool (II): Children reported practice related to COVID- 19 to assess hospitalized school age children' reported practice related to COVID-19. Results:  Total knowledge of the studied children about COVID-19 was good and total reported practices related to COVID-19 were satisfactory post preventive nursing guidelines implementation. There were highly statistically significant relations between the studied children's total knowledge score regarding covid-19 and their personal characteristics. There were highly statistically significant relations between the studied children's total practices score regarding covid-19 prevention and their personal characteristics. There was a positive correlation between the studied children's total knowledge and total reported practices between pre and post the preventive nursing guidelines implementation. Conclusion: The preventive nursing guidelines was effective in improving hospitalized school age children' knowledge and reported practice about COVID-19. Recommendations: Simple Arabic illustrative educational booklets, posters and COVID-19 plan should be produced and provided for all children in inpatient and outpatient department.