This study tests a new medicine called HLD200 for young children (ages 4-5) with Attention Deficit Hyperactivity Disorder (ADHD). ADHD is a condition that makes it hard for kids to pay attention and control their behavior. The study checks how well HLD200 works, if it's safe, and how the body uses it (this is called pharmacokinetics). Kids will take either a low dose (20 mg) or a higher dose (40 mg) of HLD200, or a placebo (a pill with no medicine). The study lasts about 9 weeks, including 4 weeks to see if kids can join, 3 weeks taking the medicine, and 2 weeks to check on safety after stopping the medicine.

• The study will last up to 9 weeks with several doctor visits.
• Children will be randomly given either the medicine or a placebo.
• Parents and children must agree to follow all study rules and appointments.