The word 'toddler' is a relatively modern English formation, emerging in the late 19th century. It is built upon the verb 'toddle,' which dates to the 16th-17th century and is of uncertain origin, though it is likely imitative or expressive of the short, tottering steps of a young child. By adding the agent suffix '-er,' the word literally means "one who toddles." This term perfectly captures the developmental stage it describes, shifting from the literal action of unsteady walking to define the entire age group characterized by this distinctive gait.

Structure: toddle (verb) + er (agent suffix) - toddle: Origin: English (16th-17th century). Functional role: The core verb meaning "to walk with short, unsteady steps." - er: Origin: Old English. Functional role: Agent noun suffix, indicating "a person or thing that performs the action."