well, my 2 are a lot younger.
dd1 has had (access to my) ipod touch since she was 3. she now has her own (school provided) ipad. dd2 has also used my ipod since she was 2, and tries to pinch a go on her sisters ipad whenever possible 
for them, the range of educational apps are great. I obviously don't know a lot about educational uses for older children.
the games are great - angry birds, doodle god etc. sudoku, chess, scrabble - all have fantastic app versions.
of course, it is a music player too. and you can access the internet via wifi (which could be a problem for older childrne, I suppose?) - so all facebook, twitter etc when in wifi range. and email.
if you are considering it, do look at the otterbox range of cases - the defender series is ace. dd1 has one for her ipad, and it is really solid, and adds a lto fo protection.