I have been in the US for a little over 40 years. When I first came, I worked in a factory in Chicago and I was TOLD by one of my American co-workers - Oh, you're Irish! I said "No, I'm not."
She said,"YES, YOU ARE! You talk just like my neighbor and she's from Ireland."
I was born and raised in Birmingham! I'm a Brummie! LOL
My children were little tiddlers when we came - 6 - 4 - and 3 months. All of them speak with an American accent. When I go home to England, my family think I speak like a Yank - but people here can still tell that I'm a furrerner! LOL I don't mind.
So - accents don't even last one generation - the children pick them up from their peers, school, friends and carry them along. But - I think that once you have gone past about 25 years old, it's difficult to erase the dialect. AND, when I get round a bunch of Brummies - I am in 7th heaven! Ow Yow doin? Aright ar kid?
IPA