This study is testing a new treatment for challenging cancers in kids: **neuroblastoma** (a cancer often starting in the adrenal glands) and **osteosarcoma** (a bone cancer). It uses special immune cells called **γδ T cells**, which are grown from healthy donors. These cells might help fight cancer better. The study will see how safe this treatment is, what the best dose is, and how well it works when used with other cancer drugs.

**Key Points**:

• **Duration**: Patients receive γδ T cell infusions on Day 6 and possibly again on Day 13.
• **Participants**: 6-24 children with difficult-to-treat neuroblastoma or osteosarcoma.
• **Eligibility**: Must be over 12 months old and have specific health conditions; cannot have had certain prior treatments.

Before joining, patients need to stop certain treatments and meet health criteria. The goal is to find if γδ T cells can improve cancer treatment results with fewer side effects. This study might help develop better therapies for these tough cancers in the future.