“Fantastic Beasts and Where to Find Them,” rated PG-13, 133 minutes. Three stars. Xenophobia. Prejudice. Oppression. Who’s up for a little escapism at the multiplex? J.K. Rowling, embarking on her new, post-Potter blockbuster franchise with “Fantastic Beasts and Where to Find Them,” has said herself that her screenplay, which she began several years ago, was informed by world events — particularly, she noted, a rise in populism around the globe. And so there’s definitely some darkness in “Fantastic Beasts,” despite its being a family film, complete with the sweetest little beasts (and bigger ones) imaginable — expect to see your kid melt forthwith over the lovable jewelry-imbibing Niffler (It’s stunning how many carats he can consume without gaining weight.) WATCH: How to make butterbeer at home. But there’s also a refreshingly light tone competing with the sinister themes, thanks especially to two exceedingly appealing supporting characters headed for a sweet confection of a romance. But first, the title: Harry Potter fans will know that “Fantastic Beasts” was a required text for Harry and his Hogwarts mates.