All types of dental x-rays used in modern dentistry are now in digital mode. Normal x-ray radiation is about 1/10th of what is used in regular conventional x-rays.
So it is very safe to expose dental x-rays for children. Protective layer like lead apron and thyroid collar makes it even safer.
Commonly used x-ray is small x-rays called IOPA and the large x-ray is called OPG (Orthopantomograph).
Bite wing is a type of x-ray used to detect cavity in between the teeth.
Even in normal children, complete evaluation of teeth and surrounding structure is mandatory at the age of six years to evaluate progress of teeth eruption, falling of teeth, pressure of permanent tooth inside the oral cavity, any future alignment issues, cavity problems, any extra teeth apart from the regular 32 teeth, absence of permanent toothy, any different type of growth or swelling inside the bone should be a evaluated.
This is a mandatory protocol in western countries like US, UK and Australia.