Why can't I down load iTunes on my iPad?

iTunes is a built-in app (it can't be downloaded), so it's still on your iPad somewhere even if it's hidden. If you can't find it on any of your homescreens or app folders, and you can't find it via the search field (pull down the centre of the home screen in iOS 7), then is it hidden by Settings > General > Restrictions > iTunes being set 'off' ?

If not then have you tried a reset to see if you can find it after the iPad has restarted ? Press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.

Check to see if it is on another page (swipe left or right) or in a folder (folders have pages now too).

Does it show in a spotlight search (swipe down from the middle of the screen)?

Check your restrictions:
Settings > General > Restrictions