Yes.
There is a big difference in articulation/pronouncing bunny & munny.
"Bunny" is a front-of-the-mouth sound using the front lips pursed together... "Munny" is a back-of-the-throat sound... said while the lips are pursed together.
In speech/talking... each sound, articulation, sounding it out and pronouncing words/alphabets etc., are achieved in age-stages. For example: a 1 year old will not master certain sounds/words that a 3 year old would, age wise AND developmental wise.
As Peg M. said, it all has to do with developing development... and the motor coordination of the mouth and tongue and lips... in conjunction with the sounds made within the mouth or throat... at the same time.
At each age juncture, their "mastery" over sounds/talking/pronouncing it... will differ. And yes, it can get confused. Even the sentence structure & tenses and nouns as well.
For example, a 2 year old might say "me like apple." But a 3 or 4 year old would say "I like apples..." or, a 2-3 year old might say "me mad..." but a 3-4 year old might say "I'm mad..."
It is all per age stages and the age juncture your child is at.
How old is your child?
I learned all of this, because my son had a Speech Therapist because he was a late talker. But he is now the most talkative one in the family! And, also due to normal natural progression per his age... his speech and sentence structure formation during talking, is totally on par now.
All the best,
Susan