The purpose of the study is to assess the efficacy and safety of ruxolitinib cream in children with Atopic Dermatitis. This is a randomized, double-blind, Vehicle Controlled study. Participants will be randomized 2:2:1 to blinded treatment with ruxolitinib cream 0.75% ,1.5% , or vehicle cream, with stratification by baseline IGA score and age. At Week 8, efficacy will be evaluated. Participants who complete Week 8 assessments with no additional safety concerns will continue into the 44-week Long Term Safety (LTS) period with the same treatment regimen, except those initially randomized to vehicle cream will be rerandomized (1:1) in a blinded manner to 1 of the 2 active treatment groups (ruxolitinib cream 0.75% or 1.5%).