Because one or both parents are citizen of an EU/EEA country, you do not need to apply for a residence permit, but you must register the child with the police or apply for a residency card for the child. This applies also if the child is born in Norway and has a Norwegian personal number.
There is no deadline for registering your child/applying for a residency card for children under the EU/EEU regulations. UDI reccomends that you register your child as soon as they have a passport.
The applicant (your child) must meet at the police station/ foreign mission. It is sufficent that one of the parents follow the child, if the other parent sign the application and the passports of both parents are attached.