Answer: Baby Mine
After what happened during the pyramid performance, Timothy Q. Mouse took Dumbo to see his mother to make him feel better. During the song "Baby Mine", Dumbo's mother rocked him with her trunk. Many other circus animals were shown sleeping with their babies, too.
The song was sung by Betty Noyes. It was nominated for the Academy Award for Best Original Song in 1941, but lost. However, the movie did win the Academy Award for Best Original Music Score.