This study tests a combination of **sirolimus** and **metronomic chemotherapy** for children with tough tumors. **Sirolimus** is a medicine that helps prevent the body from rejecting transplanted organs and may also help stop cancer cells from growing. **Metronomic chemotherapy** involves taking small doses of cancer-fighting drugs regularly to slow down tumor growth.

The study involves children aged 12 months to 30 years who have certain high-risk tumors and are in complete remission or have minimal signs of cancer after initial treatment. The goal is to see if adding this new treatment after standard therapy can help children stay cancer-free longer than just observing them after standard treatment.

• **Study Duration:** The study aims to track each participant for 2 years to see if the treatment helps.
• **Visits:** Participants will need regular check-ups to monitor their health and the treatment's effects.
• **Risks:** There may be side effects, and not all medications can be taken during the study.