I agree with Deano on this one, an open carcass is all but certain to draw them in, but if a dead rabbit slit open next to your nieces trampoline is a bit too much, you could always use 1/4lb of mince, the redder the better. In my experience works just as well!
Stay hidden, they'll be on the lookout for you don't doubt it and once you get the first the others should flock in... strangely enough!
Let us now how you get on and good luck!
Jim