I'm not sure that mitten pronounced mi-en with the missing t's is a New England thing. I grew up in New England and never heard kitten and mitten pronounced that way until a relative returned from school in Utah. She came back saying IN-surance, living room suit (not suite), jewel-a-ry and all children were kiddos. I visited my family member several times in the great state of Utah and never gave a thought to anything beyond the friendliness of the people and my first bite of funeral potatoes. Yum! I celebrate regional differences in usage which is completely different than spelling errors and egregious grammatical mistakes.
I worked with lower income families for many years and I will tell you that correcting spelling and pronunciation was low on the priority list. I remember going to a student's apartment and seeing him and his younger siblings sitting in a circle at suppertime. The lights were off and they were eating canned beans. I asked him what was going on and he said his mother was working, he was watching the 3 little ones and the lights were off to save money. That boy is now a college graduate and small business owner. There is only so much a child can absorb in the formative years. For him, it was math, science and survival.