This study investigates the effects of a combination of investigational medications on pediatric subjects with certain types of recurrent or refractory solid tumors. The purpose is to find the highest safe dose of these medications when given together, and to understand how the body processes them. Additionally, researchers will study biomarkers in blood and tumor tissues to evaluate the effectiveness of the treatment and any changes in tumor size.

Participants will undergo various study procedures, including receiving the investigational medications once daily. The study will monitor how the body absorbs, distributes, breaks down, and excretes these drugs. Biomarkers will be assessed to help researchers understand the disease and the effects of the treatment.

• Who can participate: Children with recurrent or refractory solid tumors, including specific types like Ewing sarcoma, rhabdomyosarcoma, and high-grade gliomas, may participate. Participants must meet certain health criteria, such as adequate kidney, liver, and heart function, and must not have certain conditions like untreated CNS metastases or recent invasive procedures.
• Study details: Participants will receive a combination of investigational medications once daily. The study will include monitoring for any side effects and assessing the body's response to the medication. A placebo is not used in this study.