How can a mother fortify her children while they are away from her, whether inside or outside the home?

The righteousness and piety of parents preserve their children from evil, as confirmed by the Almighty's saying: "And let those [therein] fear who, if they left behind them weak offspring, would fear for them. So let them fear Allah and speak a sound statement." Muhammad ibn Sirin used to prolong his prayers hoping that his son would be preserved, emulating the Almighty's saying: "And their father was righteous."