DC films have a reputation for being a little too self-serious. They’ve made significant strides to chip away at that dark and dour image in recent years, but it lingers even with things like “The LEGO Batman Movie.” Sometimes it’s even easy to forget that when it comes down to it, superheroes are for kids.

This makes ” DC League of Super-Pets,” a straightforward cartoon with a sense of humor about itself and an all-star voice cast, somewhat refreshing. It also could be viewed as a shameless early advertisement to get impressionable young minds hooked on the Justice League so that several years from now when it’s inevitably rebooted, they’ll have a youthful, built-in audience. But we’ll take the charitable route here considering it does come from director Jared Stern and his “LEGO Batman” co-writer John Whittington, who have managed to find joy and humor within cynical toy-hawking, fan-recruiting constructs.

After all, this is a film that gives us Kevin Hart as a shelter pup, Marc Maron as Lex Luthor, Kate McKinnon as a murderous guinea pig named Lulu, Natasha Lyonne as an ancient, libidinous turtle named Merton and Keanu Reeves as Batman. It’s impossible to top Will Arnett as the caped crusader, but Reeves makes a good case for himself delivering lines like “Batman works alone. Except for Gordon. And Alfred… and whoever Morgan Freeman played” in a way only he could.

Wearing its heart on its sleeve, “DC League of Super-Pets” opens on the planet Krypton where a cherubic baby Kal-El is being sent to earth. But he’s not alone. A puppy named Krypto (Dwane Johnson) goes along for the ride and signs up to be the future Superman’s (John Krasinski) lifelong watcher and crimefighting pal. Krypto takes his mission very seriously. In his eyes, he’s not just Superman’s best friend, he’s his only friend and things start to get a little tense when Lois Lane (Olivia Wilde) enters the picture. In his jealous rage one night (eating ice cream, watching “The Great British Bake Off” and listening to Taylor Swift’s “Bad Blood”), Krypto doesn’t notice that Superman is in distress. His beloved owner is captured along with the rest of the Justice League by Lulu the guinea pig.

It is McKinnon who really makes the movie as Lulu, a displaced Lex Luthor science experiment who has been biding her time in an animal shelter, building a device to wield the powers of orange kryptonite waiting for the right moment to strike at the Justice League. Her compatriots in the shelter are Hart’s Ace, a pig named PB (Vanessa Bayer), a squirrel Chip (Diego Luna) and Lyonne’s Merton, none of whom are ever selected for adoption (it’s always a kitten on their first day). But at least they get their freedom when Lulu’s plan works and suddenly they all have superpowers. You can guess what happens from there.

The visuals, though, are less inspired. These CG characters, especially the Justice League, are smooth and dull creatures, computer generated to the point of blandness. Wonder Woman in particular even veers into uncanny Cocomelon territory with her minimally expressive face and unfocused eyes. Perhaps the superheroes were an afterthought to their animal counterparts.

Johnson and Hart seem to have fun, too, but a fair amount of their charm as a comedic duo is lost without their physical presence — not that the audience of kids will know this or care. Parents might just be wishing they were watching this cast in live-action instead.

“DC League of Super-Pets,” a Warner Bros. release in theaters Friday, is rated PG by the Motion Picture Association for “action, mild violence, language and rude humor.” Running time: 106 minutes. Two and a half stars out of four.