If someone has chemo as a child can it make them sterile?

Yes it can: Chemotherapy is capable of damaging the gonads and can cause sterility . Many of the younger subjects can recover their fertility over a period of 3-5 years but many remain sterile for the rest of their life. It is kind of unpredictable.

Depends....: Certain chemotherapy regimens put patients more at risk at becoming infertile. The age at treatment and the sex of the patient also affect this risk. Much has been learned about how to help childhood cancer survivors retain fertility. There are fertility specialists who have expertise at assessing this type of risk and offering possible solutions.