A fixture for use in taking X-ray images of children comprising; a base including cylinder having a height adjustable piston, and at least one mounting arm. The mounting arm including a first end connected to the front wheel of a bike and a second end connected to a rear wheel of the bike. The bike including a first seat; a second seat portion supported by the mounting arm, the second seat including a back portion that is transparent to X-rays. An x-ray cassette is mounted on a swivel arm and can be positioned to take typical x-ray images of a child's torso including anterior, posterior, left lateral and right lateral. The fixture can work with any x-ray source and can work with wall mounted x-ray cassettes as well.