The Homeworld Kindergarten appears to be the main reason why the Gem Homeworld looks barren and devoid of life; by constantly exploiting their own resources to produce more Gems via the Kindergarten. According to Peridot, the constant use of the Kindergarten on Homeworld caused the planet to lose most of its resources, which led to the creation of Era 2 Gems (Gems that used fewer resources to produce and have less power). It's shown in "Off Colors" to be massive, to the point of needing a cave system in order to navigate it. The Off Colors used the tunnels as a means to escape and hide from the Shattering Robonoids their entire lives, due to their defects and being forced to isolate themselves as a means of protection. Fluorite mentions that the Off Colors have been hiding in the tunnels for eons, indicating that this Kindergarten has been out of use for a long time.
After falling to the underground surface of Homeworld in the previous episode, Steven and Lars were lead into the Homeworld Kindergarten by the Rutile Twins and met and learned about the Off Colors. When Shattering Robonoids infiltrate the tunnels, Steven and Lars help the Off Colors remain undetected by destroying the machines, which ultimately causes Lars' death.
Continuing off from "Off Colors", Steven resurrects Lars inside of the Homeworld Kindergarten and travels to Earth through his pocket dimension. Returning to the Homeworld Kindergarten, Lars discovers that he can't go through his own hair to get back to Earth, so the Off Colors decide to stay with him to find another way there, while Steven returns to Earth to retrieve help.
It is explained that the Off Colors, led by Lars Barriga, had escaped the Homeworld Kindergarten and have been on the run.
During Steven’s traumatic flashback, he and Lars can be seen in the kindergarten.