Wood – How did the sideboards come to be raised over a hardwood floor

The answer is "it depends" -- on what you need, on how well it's cared for, and how often you want to refinish it. Real wood is measured by something called the "Janka Hardness Scale" -- oak is a good choice, as it's rated at about 1300, with only more exotic woods being harder. I was told that Oak would probably be scratched by my dogs' claws, though, and I imagine that the invariable stones stuck in kids shoes will be worse. If it's possible, get real oak and make the kids take their grubby shoes off at the door... :-P

The "engineered" hardwoods are better because they're cheaper, but worse because they're not able to be sanded smooth and refinished. You'll usually see thicknesses plus a Janka measurement or an AC rating. The thinner the veneer, the more likely you are to crack through it no matter what the hardness of the veneer or the AC rating of the floor are.

For 100% composite stuff, such as Pergo and Kronotex, you'll see hardness measured on an "AC" scale that's basically a designation for how much traffic the wood is designed to bear in a residential or commercial setting. "AC2/Moderate Residential" will be too soft for your needs. "AC3 - Light Commercial/Heavy Residential" may be durable enough for your needs, but might show wear. "AC4/Moderate Commercial" is most likely what you'll need to go with, and it's harder to find and more expensive. However, it's less expensive than wood is no matter what.

Two things you didn't say... first, what kind of structure you're installing it on. Is it a wood subsurface, or is it slab-on-grade or slab basement? If it's on concrete in any way shape or form, you definitely want to go with something that is composite and less expensive. I know that you CAN install wood on slab-on-grade, but I would never consider doing it, personally. Second, what rooms is this going in? Wood floorings, regardless of composite or engineered or natural, is not good in places that will receive water on the surface or may be exposed to leaks. So the entry hall (front door and back), the kitchen, and the bathrooms are places to avoid having wood floors. I would keep vinyl or tile in those areas, or explore the wood-grain ceramics that are becoming quite popular for those areas or over slab-on-grade.

Wall to wall carpeting is usually attached to the floor using carpet tack strips around the perimeter like these

The raised tack points grip the edges of the carpet.

Once you pull up the carpet, there is probably a padding that is just laid on the floor without adhesive. If it is rubber backed, the rubber bottom surface sometimes sticks to the floor underneath. Rubber residue can usually be scraped of with a plastic putty knife without damaging the surface of the wood underneath.

The tack strip can be pried up and there will be a few nail holes per strip that can be easily filled.

The real issue will be the condition of the finish on the floor once you get to it. If there is glue on the surface, this may be difficult to remove without serious sanding. Often the finish is fine and a cleaning is all that is needed.

If the finish is slightly worn or lightly scratched, a light sanding followed by a coat or two of polyurethane should restore it. Professional finishers have a light abrading process using large buffing machines that can do this easily and quickly. However it can be done with an orbital sander and lots of time and elbow grease. Very thorough vacuuming and wiping of all dust is essential for a good finish.

If the finish is badly worn or deeply scratched, a serious sanding and refinishing is called for. Again, it can be done by the DIYer, but this is a big job, sanding with power hand tools is very tedious and the professional sanding machines are difficult to use for the novice.