I'm a step mother to 3 children and I've also got 2 kiddos of my own with my hubby.
Sometimes is been an uphill battle being a step mother....and the Disney stereotype doesn't help. (That means you Cindrella and Snow White)
I'd like to say it's easier being a step parent to kids who are older...all grown up over age 20.....but it's only slightly easier. They can sometimes be harder to get to know, and you actually have to earn their respect. Young children are taught (or they should be) to respect adults, so there is an automatic respect but not to necessarily like you. As a step parent you can been seen as someone trying to take over for their own parent, or you are automatically disliked because they think you 'stole away' their parent from their family. In some cases that is true, but not in mine.
There is almost always a defiant streak in the child to disobey. The knowledge that's put inside them that regardless of who you are, you aren't their 'real' parent.
Some children make up stories about the step parent and tell them to their 'live-in' parent. I'm not sure why....maybe it's because they want more attention, or they dislike the step parent and want them to get in trouble.
Being the extra parent is a hard job. Sometime I want to quit. It's an honest truth. I think it can be made harder when the biological parent you as the step parent are living with doesn't have much to do with the child, or even cares to be much involved. It can put an additional strain on the marriage and the relationship with the child.
I won't go into specifics with my step parenting experience, but it's a stressful job on my end.