First off, your granddaughter's low platelet count is mild. Assuming that her platelets are functioning normally, she is essentially at no increased risk of bleeding due to her low platelet count. If the rest of her blood counts were normal, in a 1-year old, the most common cause is probably a viral infection. Many viruses (which cause only mild or even unnoticed illness) can lead to a temporary decrease in platelet count which resolves over 1 to 2 months. Signs which would point to something more concerning would be if she has decreases in her other blood counts (red blood cells, white blood cells), if she develops a "petechial" rash (looks like pin-point to pencil-tip sized red spots), if she experiences nose or gum bleeding, a fever or abdominal pain. But with the more concerning causes of decreased platelets in children, she would have very low platelets and other abnormalities in her blood counts. If she's feeling well, I would recommend that she have her blood counts rechecked in 2-4 weeks. I would also ask your doctor to order a manual blood smear review (meaning that an actual person looks at the blood under the microscope rather than just having a machine count the cells and platelets). If they fail to return to the normal range, a further workup would be indicated. Until then it's something that should be followed, but at this point, it is not something that warrants getting overly concerned about. I hope this information is helpful and let me know if you have further questions or need clarification.