Naturopathically it can indicate the liver health and as the ladies above have said iron, lactose and herediatry could also play a big factor. Many kids and people have sluggish livers (Herediatry again) so one of things you can work on safely with a little one is dietary factors. Limit refined carbs,keep an eye on diary, frutose and sugars, dilute juices with water and plenty of water/veggies. Also keeping a diary or book can help you pinpoint any factors that may be helping the circles disappear or being more noticeble.