We visited the North Sea Oceanarium on a sunny day in mid-May, there was ample parking and no queue. It was fun with people during our visit.
You first enter a large dark room with several different aquariums with different species of fish. Here you can read about the different fish. Next to this room was a room with open water tanks where you could clap starfish and crayfish.
If you go up to a floor where the kids are playing in a hut, pretend that they could drive their own ship, and you could read on different screens at sea and watch movies about known storms in Denmark. Then you went to the huge aquarium, where a diver fed the fish at different times during the day, as a show, but it was in Danish, the diver has a camera so that you can see the aquarium and the fishermen when they pass through Eyes are fed.
To go outside, go through a long underwater tunnel where you can see the seals swimming. Outside, you can watch when the seals are fed, fish crabs, it does not cost anything extra. There were several different playgrounds, including a lighthouse with a long slide, a fishing boat swinging like a storm, children playing on a natural pontoon, playing with boats in the water, two sandboxes with toys in them.
The outdoor restaurant was closed, but there were plenty of tables and chairs to eat co-food, even under the roof. There are many toilets and I have experienced the place as clean and fresh. There were not that many people so we could really look at everything and the kids could play without pushing crabs and catching them without standing in line. Of course you had to go through a large gift shop before going out.
Definitely worth a visit if you have the roads. Our kids were 9,7,5 and 3 years old and it suited them all. North Sea I found on Danish ABC, but did not book anything in advance. Instead, we bought everything when we got there.