Many people run over by trains ( to mention a relatively common occurrence in Tokyo ) are put in the 'accidents' statistic chart as well, even when it is no such thing in some cases, but a clear, deliberate suicidal act. I speak from personal experience, and not just once. For many reasons, even though it's obvious for everyone and there might even be witnesses to the event, better to avoid the stigma.

Likewise in Real Estate companies having to disclose such events in their properties. Much easier to deal with an 'accident' than a 'suicide' in an otherwise perfectly good apartment.

The issue is probably underreported in every demographic, children and pre-teens included.