Dave, as a former Home Inspector and now a Catastrophic Insurance Adjuster, most of the finished basements I see have carpet. Some have had moisture problems but they had them before the carpet was installed. I think, and I don't know if I could prove it, that laying a piece of thin plastic film on the floor could show moisture where there was none. Reasoning, cold floor and warm room would cause condensation on the underside of the plastic and it wouldn't prove that it was from seepage thru the concrete. A better test would be to use a moisture meter. You could also spray or wash the floor with a mild solution of bleach, dry, lay a vapor barrier on the floor, install 2x4's every two feet, install styrofoam sheet insulation between the 2x4's, install plywood over that and install vinyl. This would give a smooth surface for the toys plus warmth on the floor and not as hard as concrete. Or you could carpet it. Either way, if you have sumps or drains in the basement, you might consider getting a sump and drain policy added on to you're insurance. If no sump or drains, then maybe a flood policy. Good luck, whatever you do.