Baby Mario
Baby Mario is Mario's baby self who first appeared in Yoshi's Island DS. In this game, the Stork is on his way to deliver Baby Mario and Baby Luigi to the their parents in the Mushroom Kingdom. However, on the way, Kamek, an evil Magikoopa, kidnaps Baby Luigi and the Stork. Baby Mario falls into Yoshi's Island and lands on the back of a green Yoshi. Kamek has predicted that the Mario brothers will cause problems for the Koopas in the future, and as such he attempts to kidnap the babies. The Yoshi brings Baby Mario to the other Yoshis, and they decide to help Baby Mario rescue Baby Luigi from Kamek and Baby Bowser.
Although in the Yoshi games, he cries a lot, he is still brave like his adult form. Though some of this is just innocence, he is couragous nonetheless.
Baby Mario is a playable character in most of the Mario sports titles, such as Mario Golf, Mario Tennis, Mario Kart: Double Dash!!! and Mario Superstar Baseball. How Baby Mario can exist in the same time period as Mario remains a mystery. This was explored to a certain extent in Mario & Luigi: Partners in Time, although Nintendo has yet to link the game to the sports titles.
Baby Mario, and his brother Baby Luigi, star alongside adult Mario and Luigi in Mario & Luigi: Partners in Time for the Nintendo DS. They ride on the adults' shoulders, and a baby takes over when one of the adults runs out of HP. Their adult versions travelled back in time to save Peach which is why they met. Luigi and the two babies often appear in the backround doing humorous things when Mario is talking to someone.
Baby Mario appeared in the new game Yoshi's Island DS. He was able to increase Yoshi's speed and break special "M" blocks. In this game he went to save his Baby Luigi and the babies from Bowser and Kamek. With the help of Yoshi and the other babies, Baby Peach, Baby Donkey Kong, Baby Wario and Baby Bowser Mario saved Baby Luigi again.
Some people believe Baby Mario is Mario's son and Baby Luigi is Luigi's son. However this has been proven false many times, but people still argue.
Mario Superstar Baseball Bio
"The elder of the baby Mario Brothers. After arriving in a stork-related calamity, he and Yoshi rescued his little bro. Though he's supposed to be Mario in his youth, you can play as both of them at the same time for some reason. He has excellent foot speed but lacks power do to his diminutive size."
Controversy
Many people disagree on the relationship between Baby Mario and regular Mario. The modern-day Mario is said to be from Brooklyn, New York, but has an Italian accent, which already makes his origins unclear. The possibility that he may have been born in the Mushroom Kingdom is even more confusing. Adding to the befuddlement is the fact that Baby Mario and Baby Luigi have been seen in numerous games with their adult counterparts, the most inexplicable of which being various sports titles (Such as Mario Superstar Baseball and Mario Kart: Double Dash!!, to name a few). Whether there is a logical explanation behind these occurrances or this is simply a plot hole created by lazy writers is, as of yet, unknown, but nonetheless, new theories will always be popping up.