Looking for input on my Denmark trip itinerary.

I have only visited Copenhagen, so I'll keep my comments restricted to that. I found a weekend (Friday evening to Sunday afternoon) adequate for checking out the city. I could have easily used more time to more thoroughly explore, but I hit all the sites on my list in that time. Using the free Citybikes helped make my time more efficient , however see my post under the "Trip Reports" section for some problems with the system.

If your children enjoy Vikings, then have an extra day in Copehagen and take the train to Roskilde. They have a wonderful museum that includes ships that they have excavated and reassemmbled as well as ships that they built using building techniques and materials the Vikings used.

For the kids, visit Bakken Amusement Park in Klompenborg (just north of Copenhagen). To see a great looking castle, do a day trip to Hillerod to visit Frederiksborg Castle.

At Roskilde there is also the Lerje Experimental Center which is a collection of recreated stone age and iron age villages. Wonderful hands-on activities like making fire and stone age cooking.
Tivoli in Copenhagen is delightful for kids as well as grownups.

What fun! A few comments - In Helsingor, check out St. Mary's. It's a venerable and ancient priory & church with an AWESOME Baroque organ (Dietrich Buxtehude was an organist there). And there might be a festival going on, too. Worth checking the schedule since you'll be locals for a week. Of course you'll see Kronborg Slot. But also great is the museum of technology, which has way cool stuff that kids will groove on. It will be eye popping for them to see old radios and gramaphones and other such moldy/oldy pre-iPod things. :-) The shipping agent's place - I had to look up the name in Danish, which is Museet Skibsklarerergaarden - is really nifty as well. You can grab a beer right there after checking out the olde tymey maritime stuff. I am an old ships geek, but I think anyone would love this place. You will find plenty to do in Copenhagen in 3 days. I am a HUGE and VOCAL fan of Tivoli - both for kids and adults - and you could actually sink the better part of a day there. You have it listed but I'm giving a shout-out b/c I've noticed there isn't overwhelming love for Tivoli on this board. Please don't have Six Flags/Disney World expectations. It's really nothing like that. It is hugely Danish, very fun, and super for people watching. The rides are antique but a hoot, and there's lots of good fair food (also some fine dining-but it is PRICY). I also think Christiania would be a great place to explore with kids. I love it - just having a wander and looking at the amazing, one-of-a-kind houses is great fun. And a quick note on Rosklide. The Viking ship museum is really a MUST see if you can get there. And the cathedral has deliciously creepy/Goth decor, so would not bore the kids. They can cruise around looking for skulls and bones. Scroll down for the awesome winged skull, as an example: http://tdeslibrary.blogspot.com

I'm sorry I'm just now responding, but I wanted to say thank you for all of your replies!

2 to 3 is great in Copenhagen. I would see Roskilde on the way to Aero (spend half a day or so there). Aero was awesome. My wife and I did Rick's recommended bike ride (18 miles give or take) and it was a great day I'll never forget. Enjoy!