The pics will look flat if the sky is cloudly, but they should not be underexposed. The fountain pics not only look underexposed but the colors are washed out. Looking back at the 1st 3 pics you posted, e.g. the teddy bear, the bear's mouth was near grey instead of close to white.
You can try shooting a few more shots outdoor in the afternoon when the sun is very bright. If the pics are still "dark/dim" then there might be some exposure problem with the camera. Not sure if your camera can display histogram, but if it is able, check the histogram after shooting a scene with balance lighting. The histogram should be quite evenly distributed. Otherwise if the pic is underexposed it will skew to 1 side.