Becoming a stepparent is a big undertaking, but nobody expects to become the sole caretaker of their spouse’s children from a previous relationship. Usually, it’s a lift between you and your partner and their ex (and maybe even their ex’s partner), which allows for quality time with their kids without the pressure of usurping the title of mom or dad. It’s healthy to want to become an adult that your stepchildren can fully trust, while knowing you can never replace the parent you’re stepping in for. 

Some steparents have to step up for their stepchildren in a way that far exceeds their expectations. A stepmother might have to take the place of their mother because their biological mother is no longer in the picture. A stepfather might have to raise his stepkids on his own because their mother passed away and their biological father was never in the picture to begin with.