Baby Peach is Princess Peach as a baby. She is a lightweight, like the other babies, who are Baby Daisy, Baby Mario, and Baby Luigi. Her boyfriend is Baby Mario and her best friend is Baby Daisy. She wears a mini version of Peach's dress.
Mario and Luigi series
The only Mario and Luigi game that Baby Peach was in was Mario and Luigi: Partners in Time. In it, her castle is attacked by Baby Bowser and the Shroobs. Baby Mario and Baby Luigi attack him. The castle is declared lost, and Baby Bowser calls in Kamek to help him. He lets Baby Mario, Baby Luigi, Baby Peach, and Toadsworth the Younger come with them.
Super Mario World series
The only Super Mario World game Baby Peach appeared in was Yoshi's Island DS. In it, Kamek and Bowser try to kidnap the seven Star Children. She gets kidnapped, but the Stork saves her and Baby Mario. However, Baby Luigi is still captured. The Yoshis help them and the other Star Children save Baby Luigi. Baby Peach can help the Yoshis that carry her float in strong winds.
Mario Kart series
The first Mario Kart game that Baby Peach appeared in was Mario Kart Wii. She is a starter light-weight character. She has high acceleration and off-road, but low speed. In Mario Kart 8, she is a light-weight default character. In it, she has high acceleration, handling, and grip, but low speed and weight. In Mario Kart Arcade GP DX, she is a playable downloadable character. She is a light-weight character who has the same speed and acceleration stats as Baby Mario.
Mario Baseball series
The only Mario Baseball game that Baby Peach appeared in was Mario Super Sluggers. In it, she can be unlocked by completing her scenario in Challenge Mode. Afterwards, she joins Peach's team. She has a high pitching stat, but low batting and stamina. She can improve her batting and stamina with Star Skills. She has good chemistry with all of the Toads besides Toadette, all of the Baby characters, and Yoshi.