Weeds still grow through tarmac, and if it gets really hot in the sun you get those little tarry bubbles which can easily get into the house on the kids' shoes. I don't think tarmac is any less hard than paving slabs if you fall off your bike!
No, no, no, not for a patio please! There are low cost slabs, using 600 x 600 'council type' slabs would be preferable and being 50mm thick they will sit reasonably well, butt jointed, on a 50mm bed of weak sand/cement.
Tarmac is not a good option for a patio/play area. Quite apart from the fact that it looks unsightly, it's easy to crack up and allow weeds to grow through if it's not laid with proper deep foundations. Also in very hot weather it can start melting, get very sticky and once on kids' clothes, can't be removed.
If you're planning to move house soon and don't want to spend a lot of money, perhaps a layer of bark chippings would be one answer as a subsequent purchaser could easiy remove them and use them on flower borders.
Get someone to build a slightly raised frame ... if you like rustic .. with some old worn sleepers .. and fill with chipped bark. Lay on black polythene or fabric to suppress weeds. Perfect for kids, easy and cheap to do .. and you can change again when you feel like it!