How do I make my garden look nice? should i dig it all up?

I have a very garden but it is all unlevel, full of weeds and nettles, and has a bush in the middle. I want my kids to be able to play safe in the garden but at the minute they cant. I was thinking about digging up the whole thing and then putting gr seed over but I have no idea what to do. Do you dig it up, weed kill it for a week and then put gr seed down? also at the back its pebbled. How do I get rid of that? will there will soil underneath? How much would it cost to pay someone to do this for me? any help will be much appreciated