Why does my 9 year old have a belly?

Understanding Your Child's Belly During Growth

A significant growth spurt typically starts at the onset of puberty, which can occur between the ages of 9 and 15, depending on genetic factors and gender. Before this growth spurt happens, children may experience noticeable weight gain as the accumulation of excess fat plays a role in facilitating growth. During puberty, the body's fat distribution may also undergo changes.