Testing the Combination of Two Immunotherapy Drugs (Magrolimab and Dinutuximab) in Patients With Relapsed or Refractory Neuroblastoma or Relapsed Osteosarcoma

Inclusion Criteria: * Patients must have a history of histologically or cytologically confirmed NBL or osteosarcoma * Patients must have: * Relapsed/refractory high-risk neuroblastoma (NBL) (defined as disease recurrence after completion of therapy, progressive disease on therapy, or refractory disease during induction therapy) or * Relapsed osteosarcoma (relapsed after frontline therapy and/or there must not be any potentially curative treatment options available at the time of enrollment) * Cohort B1: Confirmed neuroblastoma: measurable NBL/ganglioneuroblastoma (defined as those lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) as \>= 10 mm with cross sectional imaging (CT scan or MRI), or \>= 10 mm with calipers by clinical exam). Chest x-ray cannot be used to determine eligibility. Lesions must be iobenguane (MIBG) positive, positron emission tomography (PET) avid (if patient has a history MIBG negative disease) or biopsy proven NBL/ganglioneuroblastoma * Cohort B2: Evaluable NBL (MIBG and/or bone marrow disease only) * Cohort B3: Measurable osteosarcoma (defined as those lesions that can be accurately measured in at least one dimension (longest diameter to be recorded) as \>= 10 mm (\>= 1 cm) with cross sectional imaging (CT scan, MRI, or calipers by clinical exam). Chest x-ray cannot be used to determine eligibility * Cohort B4: Patients with relapsed resectable pulmonary osteosarcoma who are scheduled for a surgic…