Adjuncts only. If your child has cancer, your worst enemy is someone talking "natural healing" or "conspiracy" in order to dissuade you from accepting evidence-based treatment. When I was a kid, children with serious cancers simply died. Now all the common ones get cures more often than not. Treatments directed to comfort and coping may include meditation, physical treatments, nutritional support.
Not on their own... Holistic medicines on their own can never cure children's (or adult's) cancer. Ever. Most oncologists will work with families if they want to attempt to incorporate holistic treatments into the standard of care regimen (chemotherapy, surgery, radiation, or some combination thereof). Always ask your oncologist before starting any additional treatments - some can interfere and lower cure rates.