"Kid" was a young clinic patient in the Season 3 episode One Day, One Room. He is the son of the character Father. He was portrayed by child actor Drew Matthews.
Gregory House was stuck in the clinic on orders from Lisa Cuddy. He was bored with clinic duty and frustrated with a constant string of boring patients. He burst into the waiting room and announced he would give $50 to any person who would leave. Dr. Cuddy tried to stop him, but a couple of people, including the Father, took him up on it.
However, the Father and the Kid returned to the clinic a few hours later. House noticed them and went to remind them of their promise to leave. The Doctor who was with them said that Kid had swallowed a kitchen magnet and they were afraid it was causing an obstruction. They couldn't see its position properly on X-rays and the child couldn't be put in the MRI with a magnet inside of him. Dr. House was sure it was nothing. He grabbed a scalpel which everyone was afraid he was going to use on the Kid. Instead, knowing the scalpel was ferro-magnetic, he used it to scan for the magnet, and he finally found it towards the front of the abdomen. He realized this meant it has passed into the large intestine and would soon pass without incident. He then asked for his $50 back.