The juice manufacturers are good. They have effectively marketed the idea to parents that kids need juice. The fact is: Kids DO NOT NEED juice.
Juice is empty calories. It doesn’t matter if it is 100% fruit juice (parent’s favorite rebuttal to me), it is still just fruit sugar. Kids do not need the extra sugar. They should drink milk or water. The official recommendation from The American Academy of Pediatrics is that a child should limit juice consumption to no more than 4 ounces a day (i.e., half-a-cup at the most).
The most common reason I recommend juice is as a natural laxative for children who are constipated. The fruit sugar causes an osmotic load to the digestive system. This means that the fluid shifts into the bowel, helping a kid have a bowel movement. The other reason I recommend juice is if a child will not drink milk and I need to increase his or her calcium. In that case I will recommend a calcium-fortified orange juice.