This study is testing a new medicine called ziftomenib with chemotherapy for kids with a special kind of blood cancer called acute leukemia. Acute leukemia is when the body makes too many abnormal blood cells. This study is for kids aged 0-21 who have this cancer and it has come back or hasn't responded to previous treatments. To join, kids must have specific types of leukemia confirmed by special lab tests. They also need to be in good general health and have recovered from past treatments.

3 Key Points:

• The study will help find the right dose of ziftomenib for kids.
• Participants will receive chemotherapy together with ziftomenib.
• Participants can't have certain other medical conditions or be on certain treatments.

Participants will also need to follow specific rules about other medicines and treatments, like avoiding certain stomach medicines that could affect how ziftomenib works.