I have a WiP that takes place in Eastern Europe in the eighteen-hundreds wherein the children speak a very different dialect.
I can confirm that. I'm from Central (Or Eastern) Europe and here, even nowadays the children are speaking with very different dialects. i.e. there is a huge difference between someone who was raised in a city and someone who was raised in a village.
My experience with Betas is that if three or more (who are also experienced in your style and genre) raise questions, then listen closer. But it seems that the majority of your Betas have had no problem.
The majority have had no problems, but as the minority have had problems, I also want to meditate how to involve them and grab them with the story. Maybe only a minor change is necessary to achieve this goal.
But I think Polymath has an important point about paying attention for settled/unsettled narrative - and am still learning about that issue myself.
Polymath is right about that. But sometimes a settled narrative seems unsettled, because you want to avoid the heavy overuse "she watched", "she looked", "she said", etc, etc... (Here, in the example dialogue the story is presented via the little girl's POV). So I must figure out a method how to present these parts without overusing these "she did this and that" elements.
“What have you dreamt about this time, little one?” she (her mother) asked. (Narrative description settled to her mother instead of the girl's POV, but here I used it to avoid "her mother". But maybe this part can be solved without any tags.)
“My dreams are my fantasies, mother,” defiant and secretive the little girl said even though her soul yearned to share her strange, vivid dream with her, but not now, maybe later. (Half-settled to the girl's POV)
Grace looked around the large room. The wooden bed on the other side was empty. (Settled to the girl's POV)
“Has Aurora awakened already?” She turned to her mother. (Settled to the girl's POV)