The mere fact that children are minors does not mean that they cannot cross the border. Minors shall be subject to the same entry and exit control as adults.
Children crossing the Polish-Ukrainian border should have a passport or other document with a photograph confirming their identity or failing that, at least a birth certificate.
If children cross the border on their own and a parent is waiting for them on the Polish side, it may be very helpful to prepare a notarized authorization for the crossing of the border by minors and hand it over to the post where the border checks will be carried out. It is also worth informing the Border Guard post that the parent is expecting minor children on the Polish side of the border.
If the children will be crossing the border with a third party (e.g. a neighbour), it may be useful to prepare a notarised authorisation for that person to take care of the children and for them to cross the border.
If it is not possible to obtain a notarised authorisation, a simple written consent from a parent for the child to cross the border alone or with a third party may be helpful.
However, it is worth noting that several notaries now offer free assistance to Ukrainian citizens.
The Polish authorities declare that any person fleeing Ukraine, including children, may enter Poland. If children crossing the Polish border have a biometric passport, they can enter Poland under visa-free travel, i.e. for a period of 90 days within a 180-day period.
If the children do not possess such a passport, they can obtain a special permit from the Border Guard to cross the Polish border and stay in Poland for 15 days. In both cases, the legal residence of these children in Poland will be extended if they meet the conditions stipulated in the Act on Assistance to Citizens of Ukraine (more information here:https://ukraina.interwencjaprawna.pl/the-act-on-assistance-for-ukrainian-citizens/)