Once I register a BO as a child object, shouldn't any changes made to the child get saved when the parent is saved? Or do I need to do something special?

Here's my code:

            this.oPolicy = (Policy)this.RegisterPrimaryBizObj(new Policy());

            this.oBeneficiary = (Beneficiary)this.RegisterBizObj(new Beneficiary());
            this.oPolicy.RegisterChildBizObj(this.oBeneficiary);

Now when I make changes in the gridview that has the Beneficaries in it, those changes are not getting saved.