"Sing!" is an episode of Oobi from the second season.
Oobi and Kako join a singing group at the community center! At first, they fool around and don't want to sing what everyone else is singing. The singing teacher, Maestru, helps Oobi and Kako understand the benefits of singing along with everyone else. The boys sing a "round." — NickJr.com
Oobi and Kako are listening to the radio. They hear an opera song called "Yo To Ho" and sing along to it. Grampu walks in with the mail, which includes an invitation to join the community center. The boys are compelled to join the center's singing group. They ask Grampu if they can attend, and he happily agrees to take them. At the community center, they find Maestru, who is trying to teach his students Ray and Mimi to hit the right note. Grampu asks if Oobi and Kako can join the group. The boys sing "Yo To Ho", and Maestru agrees to let them sing with his students. Grampu leaves.
The boys learn their first song, "Row, Row, Row Your Boat". Maestru asks them to sing it in a round style. The boys sing "Yo To Ho" instead and are asked to stop. Maestru tries to get Oobi and Kako to follow his instructions, but they do not. He tells the students that they will take a short break so he can have a talk with the new singing group members. Maestru explains to Oobi and Kako that they need to sing the same song as everyone else. Kako asks if they will be singing "Yo To Ho", and Maestru tells him that they will not. The boys reluctantly agree to sing "Row, Row, Row Your Boat" instead. The interview segments begin.
Oobi and Kako sing the song perfectly. Maestru is proud of them and asks the entire group to sing. The boys begin swaying to the music. Kako asks if they should stop, and Maestru tells them that it is a nice touch. He asks everyone to sing and sway. As they do, Grampu walks in to take the boys home. He and Maestru clap for the singers and invite the viewers to do the same. Ray and Mimi ask Oobi and Kako if they will see each other again next week. The boys assure them that they will visit the singing group weekly from then on. The episode ends.