The Agreement on passport union in Scandinavia applies, but you may still be asked to prove that you are a Nordic citizen. You should therefore bring your passport or valid driver’s license.
If you have a valid passport the police recommends always to bring this, even on trips in the Nordic region. Although there is a passport union in Scandinavia transporters can ask for identification upon boarding the plane, train, bus or boat, or at check-in at accommodations. Here, the travelers should check which requirements are needed for credentials. Travelers must follow the information from the Norwegian authorities about any changes in border control.
Children traveling with their parents do not need credentials, if the parents can show identification.
Children without identification on group travel, such as sports clubs and schools, should not be held back for inspection. It is sufficient that the leader of the group endorses who your kids are before they board.
Police still encourages the children who have passports or other identification to bring this, as it both shortens the wait and facilitates control. Children without Nordic citizenship must bring a passport or other valid travel document.
Agreement on passport freedom applies countries Denmark, Finland, Norway, Sweden and Iceland. That means you do not need a passport to cross the border between the Nordic countries. It is sufficient to demonstrate that you are a Norwegian citizen.
Should you as a Nordic citizen traveling by ferries between Sweden, Denmark and Norway, you must as an adult have your passport or driver’s license ready for when temporary border control is introduced .
Source: Politi.no / Norway Today