The story Kate Crackernuts serves as a counterexample where the daughter of the evil stepparent is a loving stepsister.
The step-relationship generally stems from a marriage when the hero and heroine are at least in their adolescence.
This premise gained traction with the 1968 films Yours, Mine and Ours and With Six You Get Eggroll and the 1969 launch of the television sitcom The Brady Bunch.
Kevin and Kell is a comic strip that focuses on a blended family.
The Disney Channel animated series Phineas and Ferb also prominently features a blended family, chosen by co-creator Jeff "Swampy" Marsh in part due to its under-use in children's programming, and his personal experiences growing up in such a family.