help laying new lawn

hello I'm new to all this so sorry if something sounds stupid, i have a small garden 22 feet x 12 foot and i have just removed 4 9 foot fern trees down to roots as far as i could, also the bit of grass that is there is patchy and longer in some places so i wanted to kill off everything by laying some lawn fabric down, but i cant decide what to put on top of it can i put a layer of top soil down then lay new grass or grass seeds or is that daft idea, would it be better to wait till everything underneath dies of then lay grass on top of that, i did consider bark chippings but i will want grass eventually as we have a child that will be playing there soon can you just advise me on the best and quickest method to get some grass down either laying or seed. Thank you

 

Spray with roundup leave 2 weeks then rotovate. if needs be add a small amount of topsoil. Rake off stones and seed. Keep watered.