2 other children,; Joseph, born 1841 and Thomas, born 1843 are listed in the 1851 census at Mow Cop. In 1861 they are listed, together with their stepmother (Sophia) as being children of Job's brother John.
I assume that between 1851 & 1861 Job has died and his brother has married his widow and become stepfather to Job's children. Mary Shenton could be the daughter of either Job or John.
Thomas and Joseph are listed under John Shenton & Sophia Brereton, but it must be remembered that they are the children of Job Shenton & Mary Scott.