You're most of the way there, since both options include a D7000 with great lenses. Since you won't want to miss a great shot opportunity with your kids, the 18-200vr II would be a good choice. You probably don't want to stop and change lenses at Disneyland.
I have the Tamron 17-50 2.8, and the image quality is very good on the D7000. But for more reach, I also have a Nikon 85mm 1.8 that I have carried along as a tourist. The downside is lens changing, and the gap in the focal lengths. If you choose the 18-200 vr II, you will be giving up some low-light performance, shallow depth of field portraits, and subject isolation at longer focal lengths. You will be able to find a Tamron 17-50 2.8 used later on. With the D7000, I don't find a need for the BIM (built in motor) version of the Tamron. Other options exist for portraits, such as a Nikon 50 1.8.
Here's a vote for the decisive moment with your kids: 18-200 vrII. Your D40 is perfect for taking out biking. *technicality: you can't bike in the wilderness