Chiitan

Astro Boy's baby brother from the 1963 series. He first appeared in episode 165 "A Great Fuss Over Babies" (Japan: "akanbō sōdō" 赤ん坊騒動)

Chi-tan was created by Dr. Ochanomizu, and was seen the most in the final season of the anime. Chi-tan was created as a comic relief character. His main characteristic is his loud bawling, which can shatter things. The king and queen of Family Kingdom are distressed at not being able to have a baby. So they decide to adopt a baby robot that wins a contest. Dr. Ochanomizu participates in the contest with his robot Chi-tan, but Dr. Ochanomizu made the mistake of allowing Uran to see this robot baby, and she became very attached to him. She even tried to sabotage his chances of winning the contest, hoping that she would have him as a baby brother. To add to this, one of the other contestants abducts all the other robot babies in hopes of winning by default. Uran attempts to attract attention to the babies once she finds them,  and Astro Boy hears this. Once Astro rescues the babies, the contest begins. While the queen bends down toward another baby, Chi-tan crawls over and pinches the queen's bottom. Uran is elated, thinking that the queen would never choose Chi-tan after he had pinched her, but she does anyway. Uran then threw a tantrum, and the queen realized how much Chi-tan meant to Uran, so she decided to give Chi-tan to Uran, as she couldn't bare to deprive their family of a baby brother.