If the soil under the concrete was compacted prior to pouring, which I sure it must have been, then for sure breakup the hard pan.
I don't think trucking in that first layer of soil is such a bad idea. Use the best mix of sand and composted organics you can find as the base. At that point you will have a blank slate to plant your slice of fruiting and flowering Heaven :-)Remember to plant a variety of Nitrogen fixers and the compost plants to help bring along the fruiting plants.
Mike

Yes, I would till the soil, as deep as you possibly can. There's no soil structure or mycelial network to break up if it's been under concrete.

If you can afford to bring in lots of compost and topsoil, I would do that. Another option is to do extensive sheet mulching which essentially makes soil. You can use cardboard, newspaper, coffee grounds (which are "green" in the compost mix), food scraps, grass clippings, leaves, straw, . . . I would also innoculate everything with mycelium if possible and plant a diversity of things including nitrogen fixers, biomass producers, and things with deep or penetrating roots. (to start.)

Congratulations on the new house! What is the soil? Sandy? Clay? Loam?

If you can find a local source (A neighbor who is digging out a space for a concrete patio) for soil that is best I think. Any construction in the area? If there is, you may be able to choose sand, clay subsoil, or topsoil from nearby excavations to make your own ideal blend. (I like a 50:20:30 sand, clay, silt myself)

You mentioned a garden/play-space, what kind of traffic are you envisioning? I would hate to till the whole thing a foot down (preferably two) and have it packed back down by the kids and their friends. If you just want a lawn and some vegetable garden, you scarcely need to till at all. Scratch in grass seeds and only double dig where the vegetables will go.

I definitely like the idea of sheetmulching, and the deep-rooted perenials are of course a good idea. How picky/close are your neighbors? Sunnhemp- wonderful biomass for composting and tremendous roots, will break up hardpan, but HUGE, alfalfa, and red clover are nice, but will look a bit shaggy. (although the flowers are beautiful)

Sorry for the disorganized, rambling post.
Eric in Japan

Here is a link that might be useful: sunnhemp

The one place that I wouldn't use sheet mulch is right outside the back door, if you have toddlers, unless you can fence it off.

Sue

I had a somewhat similar situation several years ago. The biggest problem I had, apart from compaction, was that the concrete had made the soil quite alkaline. It didn't even occur to me to check for about a year, a very frustrating year garden-wise. I'd been dumping loads of organic matter on it, which would have eventually reduced the pH, but when I realised just how alkaline it was (pH 8 to 9), I added a whole load of sulphate. Things improved dramatically after that.