My advice if you are a step-mom: Never pretend you are their mother. You can always be their step-mom but never try to be their mom. Regardless of what the situation is, it is so important to respect the mother-child bond. I would also say it’s important to form a friendship, or at least an acquaintanceship, with the kid’s mom. Be her ally and ask her to be yours to when it comes to helping with her kids. Most importantly when it comes to your partner, remember that you have chosen to enter their life with their kids; respect that parent-child bond and never try to come between your partner and their children.