I am planning to put these in our playground. But that has stones laid out now. Do I need to make sure that all the stones are removed first ? Also I keep getting lot of weeds in that area. Once I lay this , will there be issue with weeds?

As long as the stones are flat, you can place our Jamboree Playground Tiles over them. If they are not, then you would need to remove the stones. Once installed, most weeds will die since there will be no sunlight and very little space for the weeds to grow.