There's usually 2 common reasons for hens to stop laying .
1. They are coming in to their moult.
2. They are fancying some chicks of their own,,so are preparing to go broody.
When were they born and what breed are they?
A less common reason for a sudden stop in egg production is something or somebody is taking your eggs.
Here's test to see if they are going or have gone off laying..
Pick your bird up, hold it under your arm head facing away from you with your other hand lightly press on feathers just under its vent..You will feel two bones sticking out, these I have always called pin bones rightly or wrongly.
If a bird is in full lay there Will be enough space between these bones for you to lay 3 fingers side by side between them . If there is only enough to lay 2 fingers the bird is going out of lay,just one finger the bird is full out of lay .
With your new pullets you can use the same method to see if a bird is coming in to lay. 1 finger space bird ain't laying, 2 fingers bird is preparing to start laying, 3 fingers bird is laying or very soon will be ..
I am talking normal sized hens here not bantams, the same principle applies but the space in bantams will be smaller, maybe 2 finger gap when the bird is laying.
If anyone can explain this better please feel free to do so :)