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She is possibly angry and using the children to hurt their father, sadly it is common. Hopefully when she is calmer things will settle down even if it is only because she wants some free time. As the children get older they will ask to spend time with your side of the family, it will be difficult to ignore a child's request and not give reasons. They will form their own opinions of their father and if she bad mouths him will soon work out what she is doing.
Very sad when children are used as weapons, it is a short window though as from about 10 upwards they can form their own opinions and loudly make them known, then there is a lot of life to have a relationship with him.