This study tests the safety of combining two medicines, **cabozantinib** and **13-cis-retinoic acid**, for children with hard-to-treat solid tumors. **Cabozantinib** is a drug that can help stop the growth of cancer cells, and **13-cis-retinoic acid** is a vitamin-like drug used to treat acne and some types of cancer. The study will find the best dose that patients can take safely.

Kids in the study must have a solid tumor not responding to standard treatments. They will take cabozantinib pills daily, with 13-cis-retinoic acid for 2 weeks each month. The treatment continues until the tumor grows or progresses. Patients will get check-ups every week for the first month, then monthly.

• The study includes frequent medical check-ups, especially in the first month.
• Participants must not have certain health conditions like severe heart problems.
• Pregnant women cannot participate, and all participants must agree to use birth control.

Doctors will monitor the medicine's effects, and participants will continue if they respond well. It's important for families to consider the time commitment and health requirements before enrolling.