From brambles to a lawn

I'm creating an area for my son to play in. It was previously full of bushes, trees and weeds and untouched for years. Iv now stripped it back and an on turfing it with medallion. What's the best approach to killing off everything that's there but not so that new turf won't take.

 

The best thing to do is dig the stumps out as it will take a long while to try and kill those with chemicals. I was going to suggest Round-up or something similar with a glyphosate content to kill everything else, unfortunately you've cleared the ground and it needs to be sprayed on foliage as it's a systemic killer. It works it's way down through the plant to kill the roots. It will also neutralise once it hits soil so shouldn't damage your turf. However, I would give it a few weeks before laying turf just to be on the safe side. If you decide to let things grow back to use it, be careful not to use on a windy day as it may drift and will kill almost anything it touches......including grass.