What sort of disease is a childhood brain tumor?

Varies: A tumor or growth, involving the brain during childhood. Can be malignant (cancerous) or benign. Almost always serious due to the brain being involved. Modern surgery , chemotherapy and radiation therapy can treat effectively in many of the cases.

Neoplasm: A brain tumor is a unrestricted growth of a normal cell that has been transformed in some way to a abnormal state. There are over 100 different primary brain tumors in children and adults--some benign and some malignant. So in essence brain tumors are not one disease but a constellation of many different tumor types.