A security blanket or a comforting plush: Why?
The need for comfort is part of the human being and some objects remind us to calm down. They secure us in some way. Toddlers need to feel close to us. They develop their sense of attachment, secure themselves with the help of a parent and develop the confidence to face the world.
And one day, they have to deal with the unknown, whether at daycare, at school or even just while you are in another room. A parent can’t always be there to comfort them, but something that reminds them of this security and, in scientific terms is a "transitional object", that connects a new situation to the comfort of the home. This object can take the form of a blanket, a soft toy or a soft doll.
It was in the 1950s that pediatrician and psychoanalyst Donald Winnicott proposed that these objects were a sign of the development of attachment. Rather than being an object to turn to instead of love and care, they were indeed, a reminder of love and parental safety. Subsequent research continued to support Winnicott's theory. One study found that children with strong ties to transitional objects have a stronger attachment to a parent and are happier than those who do not.
As the blanket will follow your toddler everywhere, make sure it is easy to wash. And maybe, think of having a replacement.