RecruitingPhase 1Biological interventionB7-H3.CD28Z.CART in Solid TumorsThe goal of this research study is to test if a new cell therapy (B7-H3.CD28Z.CART / B7-H3 CAR T cells) is safe and effective in treating children and young adults with solid cancers whose tumors have returned or stopped responding to standard treatments (relapsed or refractory) and have been identified with a B7-H3 marker. The names of the treatment interventions used in this study are: * B7-H3.CD28Z.CART / B7-H3 CAR T cells * Fludarabine * Cyclophosphamide