When my daughter was about 3 she had a cold and was using a humidifier at night. Well when I was trying to rinse it out in the sink (it was a large humidifier), my 2 year old son came by and asked me what that was. I didn't think he would understand how and why it worked so I just told him that it was for his sister's runny nose. After a long pause I thought he had just accepted my answer. But then he asked me "how are you going to fit that in her nose?"