It will depend on whether there are any current Court Orders in place particularly a Child Arrangements Order confirming where and with whom the children shall live or a Residence Order.
If only one parent has parental responsibility and there are no residence orders concerning the child, permission is not strictly needed by her to take a child abroad on holiday.
In a situation where both parents have parental responsibility and there are no residence orders or other restrictions in place, then neither can take the child on holiday outside the United Kingdom without the written consent of the other parent or any other party with parental responsibility. If consent is refused, an application to the Court will need to be made for permission otherwise the travelling parent could face criminal charges for Child Abduction.
If grandparents and other family members want to take the children abroad, permission will be needed from all parties with parental responsibility.
A parent with a Residence Order can take a child abroad for up to one month without the written consent of the other parent. If consent is unreasonably withheld then an application may be made to the Court.
In most cases permission for a child to go abroad is usually given by a Court. Often details are required stating where the child will be staying, giving the date of departure, return and details of flights along with contact telephone numbers.
Generally, if an agreement can be reached between the parties directly an application to the Court will not be necessary. However, it is always advisable to obtain the other parent’s written consent to the holiday and for the consenting parent to be provided with copy flight and accommodation details.