Commonest sarcoma in children is -
Rhabdomyosarcoma
Lipoma
Angiosarcoma
Fibrosarcoma
Rhabdomyosarcoma

Commonest sarcoma in children is rhabdomyosarcoma.
It is a tumour of Primitive mesodermal origin.
The most common site is head and neck.
The genitourinary region is the second most common site.
Other sites are extremities and retroperitoneum