As a step parent, I'm assuming you have no genetic link to your step children. Genealogy programs, sadly, do not record emotions. The only way you can be shown as the mother of your step children is if they have been legally adopted, in which case their record can show them as adopted. Otherwise, the only option I can see is to put in a short message in their notes to say that they were raised by their father and yourself following his widowhood/divorce and remarriage.
Hope this helps.