From the Super Mario Wiki
Baby Wario is the infant version of Wario. His only appearance is in Yoshi's Island DS, with other babies. He appears to be very greedy, hence why he is given a coin magnet, and that is also one of the qualities of the adult version. However, not much is known about Baby Wario other than the fact that he cries loudly and is very greedy. He is shown to be able to talk, after having argued with Baby Bowser. Baby Wario's special move is "magnetism", in which he pulls out a magnet which attracts coins. His magnet is also capable of raising metallic platforms and moving large, metal boxes.
Yoshi's Island DS
When Baby Wario was originally kidnapped, the Toadies found his crying to be very annoying, so they left him alone in World 3-5. Some time after that, Yoshi, who has been washed away by a large wave and separated from the Stork and other babies, finds him. Baby Wario assisted Yoshi throughout the rest of World 3, but he gets away from him after World 3-8, joining up with a group Bandits in hope of even more riches. Yoshi and the rest of the babies meet up with Baby Wario one last time in Bowser's Castle, having an argument with Baby Bowser. He helps the Yoshis by defeating Bowser on the back of Purple Yoshi. After the castle is destroyed and the team finds the babies, Baby Wario lands on a very large Treasure Chest filled with his treasure. However, Baby Bowser falls and lands in the treasure as well, initiating an argument over it.
Baby Wario shares many physical qualities with his adult counterpart. They both have a large yellow cap and a big, pink nose. Under his cap, brown hair can be seen. Like Baby Mario and Baby Luigi, Baby Wario wears nothing but a diaper and a hat. Since he is a baby, he has short, stubby hands and feet.
Baby Wario's cry is the loudest out of all the babies in Yoshi's Island DS. Just like his adult counterpart, he has a tendency to be very greedy, hence the magnet ability. When Yoshi and the babies get to World 5, Baby Wario is seen arguing with Baby Bowser. This gives the idea that Baby Wario's greed may lead to him being quite argumentative. Unlike the other babies, he can talk shown by his arguing. During the final boss battle, Baby Wario rides a Purple Yoshi.
Official Profile and Statistics
Yoshi's Island DS
Instruction Booklet Baby Abilities Information
With his magnet, Baby Wario automatically attracts metal (including coins) around Yoshi. Press Up on or jump to attract things above Yoshi.