how do they develop their oral languages?
Perception of speech, observe the mouth movements of others , discriminate sound phonologically
Vocabulary development
Studies related to vocabulary development show that children's language competence depends upon their ability to hear sounds during infancy. Infants' perception of speech is distinct. Between six and ten months of age, infants can discriminate sounds used in the languages of the world. By 10 to 12 months, infants can no longer discriminate between speech sounds that are not used in the language(s) to which they are exposed. Among six-month-old infants, seen articulations (i.e. the mouth movements they observe others make while talking) actually enhance their ability to discriminate sounds, and may also contribute to infants' ability to learn phonemic boundaries. Infants' phonological register is completed between the ages of 18 months and 7 years.

Children's phonological development normally proceeds as follows:
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. at what age do they start speaking? At one year
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Vocabulary development [SEP] Development in oral languages
Studies related to vocabulary development show that children's language competence depends upon their ability to hear sounds during infancy. Infants' perception of speech is distinct. Between six and ten months of age, infants can discriminate sounds used in the languages of the world. By 10 to 12 months, infants can no longer discriminate between speech sounds that are not used in the language(s) to which they are exposed. Among six-month-old infants, seen articulations (i.e. the mouth movements they observe others make while talking) actually enhance their ability to discriminate sounds, and may also contribute to infants' ability to learn phonemic boundaries.