Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com. Why are people still getting polio in some countries and in not others? – Mia, age 9, Centennial, Colorado On a busy street in Karachi, Pakistan, a healthcare worker kneels down so she’s eye to eye with a toddler. She squeezes two drops of liquid onto the child’s tongue.