Exception for public institution
According to the DPA, the conditions mentioned in Article 6 of the GDPR regarding legitimate interest do not apply to public institutions.
Children’s consent
In Denmark, the age at which a child can provide a valid consent is reduced to 13 years old (DPA Section 6(3)). If the child is under 13, the processing is lawful only if and to the extent that the child’s responsible (DPA Section 6(3)).
Guidelines
The Data Protection Agency has published a guideline on consent (in Danish): https://www.datatilsynet.dk/media/6562/samtykke.pdf