at what age do they start speaking?
At one year
Vocabulary development
towards meaningful speech as infants grow and produce their first words around the age of one year.
ways in which infants learn the meanings of new words Infants must be able to hear and play with sounds in their environment, and to break up various phonetic units to discover words and their related meanings.
wiki:7173472
Vocabulary development [SEP] Introduction
Vocabulary development is a process by which people acquire words. Babbling shifts towards meaningful speech as infants grow and produce their first words around the age of one year. In early word learning, infants build their vocabulary slowly. By the age of 18 months, infants can typically produce about 50 words and begin to make word combinations. In order to build their vocabularies, infants must learn about the meanings that words carry. The mapping problem asks how infants correctly learn to attach words to referents. Constraints theories, domain-general views, social-pragmatic accounts, and an emergentist coalition model have been proposed to account for the mapping problem.