Is cord blood good for other children?

Yes. The cord blood contains multipotential stem cells which can be transplanted to other children with certain medical conditions, e.g., mucopolysaccharidoses.
Depends on question. Depends the intention that it will be use for.
Depends on question. Cord blood as a source of stem cells is obviously best suited to the needs of the child it came from. However, some programs have begun collecting cord blood for storage that would act like a blood bank and be available for others. Other kids in the same family may or may not be a close enough tissue match to use them safely. If enough cord bloods are saved, more people could get needed treatments.