We spent the better part of a week on the Norh Shore a few years ago, but not with our kids. We were in Pupukea, not far from Haleiwa.
There are some surfing contests held nearby while you’re there (schedule). We watched one for a few hours. I also took a surf lesson at Turtle Bay. The resort was the setting for Forgetting Sarah Marshall, which you should definitely watch before you go if you haven’t already.
The point they jump off in the movie is right there in Laie. It didn’t look very safe when we were there in November, so no jumps for us.
There’s lots of great hiking in the area. We did a lot of vertical hiking, but the Keana Point trail is flat and you may see the rare monk seals, nesting albatrosses, and some other cool wildlife out there. It’s all fenced off with a fine mesh to keep the mongoose out (they like the nesting bird’s eggs).
The Dole plantation in the middle of the island is a good stop on the way – the pineapple soft serve is Yum.
If you spend any time in Honolulu, there’s a short rainforest hike to Manoa Falls that the kids could handle.
Should be a good time of year for whale watching. We’re spending most of February in Hawaii this year – bummer we’re not overlapping. Not sure how much time we’ll spend in Oahu, but probably at least a week or so. Also planning to see the Big Island and Kauai.