Yes, you can. The law of Ukraine establishes that during martial law, men who have 3 or more children are allowed to legally leave the country.
For an unimpeded departure with 3 children, it is necessary to have 3 birth certificates in which the man who plans to go abroad is indicated as the father.
To cross the border, you must also have:
marriage certificate;
court decision on divorce;
decision of the guardianship authority or certificate of the father of a large family.