As children grow during their first few years, may of them will start sucking their thumbs or fingers. There are a number of reasons why babies and toddlers do this. First, infants enjoy putting nearly everything in the mouths, so this is a natural extension of that habit. Second, it’s worth remembering that babies find it calming. Sometimes, it’s their way of gaining a level of comfort in unfamiliar environments. Other times, it has a relaxing sensation; it reminds them of being within the womb and often helps them go to sleep more easily.