If the man has the sicklecell trait, do that mean all his children will have the trait too?

No: Sickle cell trait means that one is a "carrier" of the sickle cell gene. It takes two copies of the sickle cell gene to manifest sickle cell disease. If a man has sickle cell trait, he may pass the sickle cell gene or the normal gene to his offspring - meaning 50% risk that he will pass on the sickle cell gene. The offspring's chance of inheritance also depends on the status of the mother!