Since tetralogy of fallot is congenital will all of our children have it?

No. In most cases if one of the parents, or a previous child, has tetralogy of fallot, there is about a 2-3% risk of another child having the defect.
Congenital= at birth. The term as derived from it's root means with birth, or present at birth.It does not mean every child you have will have it.The genetic influence on heart formation is located on several chromosomes. In practice, the risk of a second child with ANY (there are many) form of congenital heart defect is about 3-4%.The risk of the same defect is minuscule.