Can a child donate bone marrow to a parent? At what age would a child have enough to donate?

Not for the parents. A child is not a good donor for his/her parents. A child has half genetic pattern from his mother and another half from his father. So, a childl will not be a full match for the parents. It'd be better for the parents to get a donor either from their siblings or from unrelated donor or from cord blood donor. Pediatric donors are only utilized for autologous collection or donation to sibling.