The Mane Six and Spike, along with Gabby and Gilda, are transported to the time of the Ice Age to help a mammoth, a sloth, and a saber tooth tiger return a human baby to his people.
The Cutie Mark Crusaders feel like they aren't being taken seriously by anypony because they are children. To prove themselves, they join the Mane Six on a new adventure to the town of Bikini Bottom where they meet a very energetic talking sponge