Tongue sucking is one of the common oral habits seen among children. It is normal for infants to suck their tongue, thumbs or fingers. It gives them a form of comfort or emotional security but when this habit goes beyond the age of 5 years when the permanent teeth start to erupt, then it can cause dental problems such as the teeth being out of alignment. You do not need to worry or do anything for now. As she grows older you will need to encourage her to stop by positive reinforcement that is giving rewards on days when she does not suck. Punishments, scolding and nagging will not work because it is a security problem. I hope you find this very useful.