Basement refinishing

My husband and I are considering putting in a carpet in our basement in order to finish off the room as a playroom for our kids. I don't know whether or not we should put in a small subfloor first before the pad and carpet or whether we can put the pad and carpet directly onto the concrete. It is fairly dry down there and in the 3 years we have owned it we only had 1 small spot of moisture near the bulkhead after days of driving rain. We do run a dehumidifier down there all summer. I am concerned about mold growth in a basement though, and since this is to be used by kids, I don't know what the current trend is to prevent that. Are there vapor barriers that are used now for this purpose? Any advice you can offer is kindly appreciated.

Framingham, USA
I would suggest you start by performing a very simple test.

Take a sheet of plastic (shopping bag without holes will be fine) about 1x1ft (or larger). Clear an area of the slab from all debris and paint/stucco/etc. Using a "duct tape" secure the plastic to the floor around its edges. The idea is to seal it in a way that water vapor will not be able to escape from under the plastic.
Leave the plastic for at least 2-3 days and watch for condensation. A small amount is expected, but if you can actually see drops of water you will know that there is a significant amount of moisture coming through. Make sure that the temperature and humidity in the room during the test are similar to what will be the condition when in use. More moisture will come through when the air is drier and warmer.
Based on the wet spot you found I would expect to see significant condensation. Make sure you test a few locations including the area where the wet spot was.
If that is the case then you have a problem. Carpets and vinyl floors should not be installed when the "vapor transmission" exceeds a standard value (3 lbs for 1000 sq.ft. in 68 hrs) in the standard "moisture dome" test (which is a more complex and accurate version of the test above). Any installer that does not test is failing to meet the standard requirements by the manufacturer and there is a good chance that the glue will fail and mold will develop.
If you have excessive amount of moisture coming through then the best option will be to leave the concrete uncovered or use concrete/ceramic tiles without a moisture barrier. These tiles "breath" and will allow the moisture to escape into the air where the humidifier will take care of it. Carpets and vinyl will trap the water and create a mold hazard.
There are some products that claim to seal the concrete from the inside. A few (very few) actually seal most of it if applied professionally, but the moisture pressure from outside is high enough to drive it through most sealants. It will be expensive to apply and I doubt that it will be covered by any warranty. I suggest you look for professional installers and ask for their opinion. Search the Internet for a product called "Xypex" and I am sure you can find installers in your area.
Hope this helps. Feel free to ask again if something is unclear. Let me know what happened with the plastic test.

Good luck
Follow up question:
Attached is your suggestions to my wife for testing our basement moisture. Given most of the basement - in the finished side - is painted, I executed the test you suggested on the unfinished side of the basement. The plastic sheet (dome test) was run for 5 days - rain did occur during this time. No moisture was present under the plastic sheet!
The water by the basement door my wife spoke of is due to a rusted out drip edge on the bulkhead door that has leaked if snow thaws on the door frame (soon to be fixed too).

Based on our results - we will pursue a carpet company to install a carpet in the basement. We will continue to run our de-humidifier during the humid months. Are some carpets and/or pads better suited for basement use?

Another question:
We are looking to install a stamped concrete front walk to simulate a gray cobble stone appetence. Do you have knowledge in this area to help us select the best techniques when searching for an installer. We have questions re: fading?, snow-melt/salt?, maintenance, durability. Any insight and suggestions would be appreciated. We live in Framingham, MA - is it too late in the season to start this project? So far we have called 3 installers and only one returned our calls - who still has not dropped by as was planned.
Nice to get the follow-up.
I am glad the test was negative. Makes life so much simpler...

As for the carpets - the local suppliers would know better than me; and the same goes for the local conditions for the concrete work.
Weather becomes a problem when you have heavy rain on external concrete, when fresh concrete freezes, and when the base is muddy. Proper planning and precautions will probably allow concrete work at this time IF the contractor knows what he is doing.

Concrete can be colored in two basic ways:
1. Add the pigment to the mix during batching so that the whole load has a uniform color.
2. Sprinkle the pigment on the surface so that it only penetrates the top. You probably save some money this way, but the color will not be as uniform or fade-resistant as the first option.
In a thin slab application I would prefer the first method.

You may also choose to leave the natural gray concrete color and avoid this complication.

Snow melting and salt should not be a problem for un-reinforced concrete. Only when you have rebars inside you need to worry about corrosion caused by salt. Make sure that the surface drains away from the slab so that water do not pond inside the grooves of the texture.
Wow! That is good information! I will follow-up with the website info you included and with the City of Madison.
I had a question about the glaze I remember atop the stones in Madison. Is that the sealant or is there some special coating like gives it that sealed in look? Is it possible to send you actual photos of the drive for you to look at? Then you can see in detail what I'm talking about. Also, the number of cracks have multiplied, there're about a dozen now. Our general contractor did considerable renovation on our house and subcontracted the drive. The general contractor has committed to having the drive redone and I believe there is no question that will happen. The tougher question is whether or not the subcontractor who poured it originally can meet a higher standard. This is why I want to get as clear as I can on what the specs look like for a superior result. As far as the stones, I don't think they were unusual for a job of this sort, they just seemed to stick out...maybe  because that sealant wasn't applied? Thanks again for you help.
What kind of work do you do?
The glaze you saw in Madison is probably some coating sprayed-on. There must be many brands and your contractor should know. The additional cracking is to be expected under these conditions.

You are welcome.