In case my description doesn't make sense (likely, although I know what I mean lol) here is a quick drawing I did to explain lol.
Make sure you give them lots of toys and fun things to keep them occupied as well. Although as young pups they will most likely sleep a fair bit.
And here is a link to somewhere to buy puppy play pens from for a decent price.
24" 8 Panel Pet Dog Puppy Enclosure Exercise Play Pen | eBay
Leaving pups all day unattended in a backyard can be dangerous, if they are in the backyard they should still be confined to an area which you have puppy inspected to make sure there is nothing for them to hurt themselves with. I have heard some seriously disturbing stories of puppies dying because they have been left unattended in backyards.
And here is a link to some youtube videos on puppy confinement that might come in handy.