Effective analgesic and sedation management require an objective evaluation of sedation level. The COMFORT Behavior Scale (CBS) is an instrument that has been validated in several languages to assess the levels of sedation in children. This evidence-based practice was implemented to identify the validity and reliability of the CBS instrument in assessing the level of sedation in children. The methods that used were Population, Intervention, Comparison, and Outcome as well as Plan, Do, Check, and Action with a descriptive analytic design using a cross-sectional approach. 51 purposively selected children ages 1 month to 18 years who received analgesic and/or sedation therapy were assessed for their sedation levels using CBS and the Nurse Interpretation of Sedation Score (NISS). The data were analyzed using the Mann–Whitney U test to measure the concurrent validity; each item was analyzed using Pearson correlation; inter-rater reliability was measured by the Kappa coefficient; and the internal consistency was measured by Cronbach’s alpha. The results showed there was no significant correlation between the levels of sedation assessed using CBS and NISS (p = 0.118; α = 0.05). Six items in the CBS instrument were found to be valid (r = 0.348–0.813). The Cronbach’s alpha for CBS was 0.873. Thus, the Indonesian version of CBS is valid and reliable in assessing sedation levels in children. Nurses play an important role in objectively monitoring the level of sedation by using valid and reliable instruments to improve the nursing care quality and collaboration in sedation and analgesic management.