Children appear throughout the show in "interview segments," a portion of each episode where the puppet characters ask real kids and their families about the episode's topic.
The children don't show up in the main stories, but they are an integral part of every episode, appearing in "behind-the-scenes" style interviews with the puppets. The interview segments are often played as transitions between scenes or at the end of an episode to recap the topic.
Oobi, Uma, and Kako are usually the "interviewers" in these segments. In episodes where Uma and Kako don't appear in the main story, they are usually included in the interviews. Grampu and Inka did a few interviews over the course of the show, but they were featured much less than the others.
In addition to the interview segments, a group of kids appears in the ending credits, making their own Oobi puppets and playing with them. Although actual humans never appear in the main story of an episode, humans in general are briefly visible in "Chopsticks!"—in the hall of the Chinese restaurant, humans can be seen in photos of Shanghai.