This is a great challenge. We had our camera for about 6 months and then tried to create a framed photo collage for our wall in our house and realized that we didn't have any vertical photos!! We had a vacation planned after that and made a point to turn the camera. We bought a grip that has the shutter button on it so we can comfortably turn our camera vertically. We came home with way too many vertical photos, but it balanced out the months of horizontals we'd taken.
Now it is second nature for us to shoot both horizontally and vertically. You can frame a shot much more appropriately if you think in terms of both. I'll try to take some new verticals this week.
Here's an oldie to tide you over.
Ok, one more that isn't of my kids: