A Phase 1b/2 Study to Investigate the Safety, Efficacy and Pharmacokinetics of Administration of Subcutaneous (SC) Blinatumomab in Pediatric Participants With Relapsed/Refractory (R/R) and Minimal Residual Disease Positive (MRD+) B-Cell Precursor Acute Lymphoblastic Leukemia (B-ALL)

Inclusion Criteria: * Age ≥28 days to \<12 years at the time of informed consent/assent. * Lansky Performance Status (LPS) of ≥ 50%. * For Phase 1b and Phase 2 cohort in participants with R/R B-ALL: * Participants with B-ALL relapsed after or refractory to any line of treatment including allogeneic hematopoietic stem cell transplant (HSCT). * Greater than or equal to 5% blasts in the bone marrow (BM) is considered as relapse in the BM. * For Phase 2 cohort in participants with MRD+ B-ALL: * Participants with MRD+ B-ALL must have between ≥ 0.1% and \< 5% blasts in the BM. * Prior CD19-…