An Efficacy and Safety Study w/ Azstarys® in Children 4-12 Years of Age With ADHD

* Screening Period (Visit 1) Subjects will undergo a screening period up to 30 days prior to entering the Treatment Period. * Double-Blind Treatment Period (Visit 2 through Visit 6, approx. 28 days) Eligible subjects will be randomized in a blinded fashion to Azstarys® or placebo at the start of the Treatment Period. Randomization will be applied separately in each cohort and stratified by gender. * Cohort 1: Subjects 4 and 5 years (\<6 years) will start at 13.1 mg/2.6 mg or matching placebo and may be titrated up or down to doses of 13.1 mg/2.6 mg, 26.1 mg/5.2 mg, or 39.2 mg/7.8 mg Azstarys® or matching placebo approximately each week through Visit 5 (Day 21) * Cohort 2: Subjects 6-12 years (\<13 years) will start at 39.2 mg/7.8 mg or matching placebo and may be titrated up or down to doses of 26.1 mg/5.2 mg, 39.2 mg/7.8 mg, or 52.3 mg/10.4 mg Azstarys® or matching placebo approximately each week through Visit 5 (Day 21) Subjects who participate in Cohort 1 and successfully complete the Treatment Period will have the option to participate in a 12-month open-label safety study with Azstarys®.