Tiny Titans was an Eisner Award winning comic-book series (2008-2012) featuring the Teen Titans' characters. It began with the "original" Teen Titans (Robin, Kid Flash, Aqualad, Wonder Girl, Speedy, Beast Boy, Cyborg, Raven, and Starfire) but eventually expanded to include most of the DCU "young" characters.
In Tiny Titans #31, the kids were hanging out with Superboy and Supergirl at the Fortress of Solitude when the Legion of Super-Heroes appeared from the future.
Art Baltazar and Franco were the creative geniuses behind this series, which was a light-hearted, fun look at the young kids in the DC Universe. The Titans attended Sidekick Elementary School. Their principal was Deathstroke the Terminator. Darkseid was their Cafeteria Lunch Lady. Lobo was their Phys Ed teacher. Their mentors never appeared in the series per se; when they were drawn in, they were only shown from the neck down (similar to the way that no adults ever appeared in PEANUTS).
There was also a kiddy version of the Fearsome Five, which included Psimon. Several characters got him and Brainiac mixed up, which led to the introduction of the actual Brainiac. But because this was Tiny Titans, we met basically every version of Brainiac, from the Silver Age original to Brainiac 13 and even Brainiac 8. And of course, Brainiac 5 from the Legion.
Here is their appearance in its entirety. Enjoy! (That's Wonder Girl Donna Troy in the winter coat, and Kon-El's Bizarro and Psimon at the end.)