Romantic movies are great - when they work. Both Zac Efron and Nicole Kidman are also fine actors - when they have good materials to work with.
Unfortunately, this movie doesn't work for me. The premise is ok - it's par for the course for romantic movies, and having a big age difference isn't a problem - it can actually be done well: think, "Harold and Maud".
The issue is that I didn't really sense great chemistry between the two characters. The setup just didn't land. Everything seemed forced to go along with what the plot requires. I think a different script could have made a big difference.
Which is ironic, given a plot of the movie.
"A Family Affair" is simply not funny nor romantic. Joey KIng's character just comes across as bitter and hateful, rather than being a humorous obstacle to Efron's and Kidman's characters that she really needed to be.