Small children take time learning how to produce the consonants in their native language. Often, they replace one consonant with another. It seems this is often about their system for producing sounds, not about their system for perceiving and distinguishing sounds.
Here is a good recent illustration from my grandson (aged 4 years, 1 month). After bedtime one evening, he emerged from the room he and his cousin were sharing. He was carrying 2 cups. Here is the ensuing dialogue:
- Boy: I want a brink.
- Mother: Do you want a brink?
- Boy: No. I want a brink for me and [name of cousin] to drink.
Several pieces of this exchange are typical:
- he replaces one consonant [here: d] with another [here: b]
- he can perceive the difference between an adult producing the adult pronunciation and an adult imitating his pronunciation, and he rejects adult attempts to imitate his pronunciation. He would accept an adult saying /drink/, but did not accept /brink/.
- after an adult tries to persuade him to use the adult pronunciation, he persists with his own pronunciation.
- he is capable of producing the adult pronunciation in some contexts. He displays this spectacularly in this case by using the adult version /drink/ later in the very same sentence, though in a (slightly) different context.
The way small children produce consonants seems to be more about their production systems than about their perception systems. This exchange provides more support for that view. I have discussed this before at Learning some English Consonants – Language Miscellany and Learning some English Consonants (2) – Language Miscellany