Ukrainian citizens can enter Romania with a short stay status by presenting a biometric or simple passport at the Romanian border crossing point. Those who apply for asylum in Romania can also enter the country based on another type of identity document (national ID card, birth certificate, etc.) or on the basis of the declared identity, without an identity document, for humanitarian reasons.
Ukrainians traveling with children should also carry an identity document of the minor or a birth certificate. Unaccompanied children can also cross the Romanian border from Ukraine.
You can get current information about the situation at different border crossings here:
https://www.aid4ukr.com/get-help/waiting-times-at-the-borders-of-ukraine
Source:
https://www.romania-insider.com/solidarity-ukraine-romania-refugees-2022