In the episode 1, Zequinha climbs inside one tight pipe and ends up in Mau and Godofredo's lair in the sewers. A real-life child doing that would seriously risk being stuck inside the pipe. Dr. Abobrinha does the same in his debut episode and ends up visiting Mau and Godofredo, too.
When Biba explains the four operations to Zequinha, she touches the subtraction button in Nino's machine and says "1 Zequinha - 1 Zequinha = No Zequinha". Seeing as the machine can apply the 4 operations on people, th1ankfully she did not demonstrate that one on Zequinha or he would likely vanish forever.
Pedro, Biba, and Zequinha will likely grow up and become adults while Nino stays as child possibly for centuries. Nino's friends are probably going to die of old age while Nino stays a child.