It would be better to settle this out of the court. It wouldn’t be right to drag kids to the court. Talk to her on this topic. Have a good conversation. Try to find a mutual solution. Try to resolve the problem. She must have a reason why she wants to separate you and your kids.
Or else you may file a child custody case under guardians and wards act and also file an application for visitation rights as an interim relief.
But usually, father don’t get the custody if the child is not 13 years old or above. Or if the mother is not capable of raising a child.
So, you need to think about this matter carefully and take action accordingly.