| if you're intending it as a playground- I'd avoid the herbicides. just on principal, even if you don't believe the arguement that such things aren't as biodegradeable as they claim. in general- rake away the existing mulch (you'll get some of the weeds as well) put down 3-5 page deep layer of newspaper, wet with hose, repeat until you have 10-12 sheets down everywhere, wet with hose one last time, and then bury it in 3" of fresh mulch...I prefer the ground mulch to the wood chips, but that's a matter of personal preference. I'm slowly reclaiming a yard left fallow for a decade with this method, and it's working better than any other method I've tried. | 
