If two parents have sickle cell trait, what will their children have?

Three possibilities. They each carry a pair of sickle related genes (one normal one bad), one of which would be passed to any child. They could have all affected sickle cell kids, all with no sickle genes, all trait or some mix of the three. The risk percentage is a confusing concept. Just because you have inly 25% risk of a SS kid doesn't mean it comes out that way, every conception is a separate risk & all can be SS.
Varies. Sickle cell disease is a recessive disease. That means you have to have two of the disease genes to create the disease. Because you both have the trait (ss) that means there are 3 possibilities for your baby. 1) ss sickle cell disease - 25% 2) ss-sickle cell trait-50% risk 3) ss-no sickle cell mutation-25%. Hope this helps.