Leo made a machine. A time machine. That malfunctioned. 5 year old versions of Percy, Annabeth, Hazel, Frank, Piper, Leo, Jason, Travis, Connor, Thalia, Nico, Rachel, Octavian, Reyna, and Bianca appeared in CHB. The teenage versions have to face their greatest challenge yet, babysitting their younger selves until the 5 year olds travel back to their own time. (Disclaimer: I don't own any of the pjo/hoo characters. They belong to Rick Riordan. I own the plot and a few characters I created.)