Answer:
You treat the 20 children with less serious illnesses.
Step-by-step explanation:
This really depends on a variety of conditions, such as where you are, what resources are available, to name a few. Terminal cancer cannot be treated, and so there is no point "treating" them other than putting them in hospice care. As such, it would be out of your duty anyways as hospice care is typically provided by hospice-oriented services.
As a doctor, your duty is to maintain and restore human health. If you cannot do the two for a terminating patient, then you should focus on the next generation.
Of course, this is not as easy as choosing one or the other. It entirely depends on what kind of doctor you are, where you are treating them, and what kind of treatment and/or services are available at the time. If all can be provided, you can outsource and treat all of them. So it really depends.