This study checks if a medication called enlicitide decanoate can safely and effectively lower bad cholesterol in kids with heterozygous familial hypercholesterolemia (HeFH). HeFH is a condition where cholesterol levels are too high. The medicine enlicitide stops a protein called PCSK9, which helps lower cholesterol levels in the blood. The study also wants to know how enlicitide works in a child's body over time compared to a placebo, which is a fake treatment with no medicine.

To join the study, kids must have a certain level of bad cholesterol and already be taking cholesterol-lowering treatments like statins. Some kids can't join if they have other serious health problems or have taken certain other cholesterol medicines recently.

• The study involves taking a new medication and comparing it to a placebo.
• Participants should be on a stable cholesterol-lowering treatment before joining.
• Children with certain medical conditions are not eligible.