Tell me if there are any legal regulations, documents to extend the vacation ...?

Yes, there are such legal norms.

If after the end of leave to care for a child before the child reaches the age of three, the child needs further home care, the employee has the opportunity to take care leave for a child up to the age of 6 at will.

After the end of leave to care for a child before the child reaches the age of three, an employee can apply for leave to care for a child up to 6 years old. This leave is not granted to a person in a mandatory manner, but only in the case when the child needs additional home care.

According to part four and part six of Article 179 of the Labor Code of Ukraine, as well as parts two and three of Article 18 of the Law of Ukraine "On Vacations", an enterprise, institution, or organization may, at its own expense, provide one of the child's parents with leave without salary for childcare for a longer duration.

In accordance with clause 3 of the first part of Article 25 of the Law of Ukraine "On Vacations", leave without pay is granted at the request of the employee in a mandatory manner to the mother or other persons specified in the third part of Article 18 and the first part of Article 19 of this Law, in the event that the child needs home care, - for the duration specified in the medical report, but no longer than until the child reaches the age of six.

To receive leave to care for a child under 6 years of age, an employee must submit an application for such leave and a medical certificate. The form of primary accounting documentation No. 080-1/o "Certificate on the need of a child (disabled child) for home care" was approved by the order of the Ministry of Health No. 430 dated 11.06.2012. (https://zakononline.com.ua/documents/show/327492___327557 )