Penelope Leech, child psychologist, says:
Though your toddler's stacking, grouping, and sorting behavior may strike you as odd, it's actually perfectly normal for a child this age. Indeed, noticing the similarities and differences between objects and learning to group like with like is one of a toddler's most important cognitive tasks. Granted, her fingers' constant sorting, arranging, and grouping activity may seem like a tick, but remember that she must first do this work with her hands before she can do it with her brain.
If you watch your child closely ? with pleasure rather than anxiety ? you may notice her carefully separating her soft toys from her dolls, putting them into neat rows, and perhaps even dividing them into smaller subcategories (the baby dolls in one row, for instance, and the Barbies in another). If you're lucky, you may even witness her contemplating higher-level dilemmas, such as whether the apple should go with the ball (because they're both round) or with the cookie (because they're both things to eat).
Obsessive-compulsive disorder (OCD), on the other hand, is debilitating rather than empowering. Instead of using organization to gain an understanding of her world, a child with OCD uses her compulsion to keep the world ? and the extreme anxiety and fear that it causes for her ? at bay. She may stay in the bathroom for hours and wash her hands until they're raw, for instance, or not be able to leave the house until she's completed a complex series of rituals. These obsessions and compulsions tend to get in the way of social interactions, interfere with normal activities, and are often accompanied by sleep problems, depression, and quirky eating habits.
Rest assured, too, that OCD is extremely rare in children, and seldom shows up before the teen years. The behavior your child is exhibiting is not OCD but the sign of a normal ? and completely healthy ? cognitive advance
Hope thsi reassures you~!