Copenhagen first week of September

I think he would love the Experimentarium (now in Hellerup). It's a big, hands-on science museum with lots of educational games, etc.

If you did a day trip to Helsingor, you could go to Kronborg Castle (famous as the Shakespearean home of Hamlet). In the town, there is also an excellent maritime museum (the M/S Maritime Museum) which I think he would also love.

Rosklide is about 20 minutes away by train, and has an awesome viking ship museum. It was one of our favorite things in Denmark, and he'd be sure to love that. They have reconstructed portions of viking ships discovered there, and then also have a working ship building area where they use traditional viking techniques and tools. There was a lot of stuff geared towards kids here.

In Copenhagen proper, I think he'd really enjoy Tivoli and a canal tour for sure. "Running" up the Rundetaarn should be fun too, and I wouldn't miss the Rosenborg Castle and its gardens. Also, don't miss the ubiquitous bakeries, which I'm sure kids would love.

The best part about all of the above as that the adults will enjoy it all too!

Add Bakken - The worlds oldest amusement park - and http://goboat.dk/en/.

If you visit Rosenborg Castle be sure to be there 11:27 when the royal guard starts it's walk to Amalienborg.

Thanks! We did some of this stuff when we there a decade ago but looking forward to sharing it with our son! Curious to know the usual weather for the first week of September?

Of course there is no way of telling what the weather will be, but for the past couple of years, we have had quite nice weather in the first week of september, sunny and around 20-25 degrees celsius. However I would pack rain gear and some warm clothes as well.

I was there for the first week of September two years ago and the weather was great! Apparently we were quite lucky with very mild, sunny weather and only one drizzly day. Nights were cool and days were in the 72 - 78 degree range. Again, we were told many times that the weather was really exceptionally nice so maybe you'll get lucky!
Would he enjoy the crown jewels in the basement or Rosenborg castle? The park surrounding the Kastellet fortress would be really fun for a little kid with many grassy hills to run up and roll down and, of course, the fort itself. If he has the patience for it, he might enjoy a boat ride out of Nyhavn.

Again, thanks for all for the suggestions!

Tivoli Gardens for sure. He'll love it. There is also a good aquarium there near the airport. Great exhibits, nice venue.