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At this age, she is telling them that it's time to stop nursing and she's separating herself from them.
Now it's time for you take an additional step and give her the means to do this.
You need to separate them. Put mom in a different room with her own litter box and get those kittens weaned.
Don't forget that this is a good time to spay mom! She will go right back in heat if you don't.
Let me know if you have more questions.