I think about this frequently. I let my kids have access to lots of media. They get TV time every day, and they get tablet/computer game time. I actually am a big fan of media as a learning mechanism, and I swear Starfall taught my daughter to read at 3, fluently by 4.
There was an interesting article in this months Atlantic Monthly about the Tablet generation. it's amazing to me that the Ipad is only 3 years old. It's crazy because I swear it has always been in our house, and it has, as hubby brought one home from work immediately. We now have something like 6 tablets in our house --all his companies. My 3 year old son even has an old phone to play games on! Since hubby is in computers/technology, media is everywhere in our house. It's hard to tell the kids they can't play with a tablet or phone when we are always on ours.
I'm a big fan of letting my kids kind of find their own happy medium. They use to watch 60 minutes of TV, but 90 minutes seems to be the right amount. After 90 minutes, they are ready for a snack and to run around. Less than 90 and they are tired and whining for more TV. Interestingly enough, hubby and I aren't big TV watchers. We only own 1 tv, haven't had cable for more than 2 years out of the last 12, so it's not like TV has a big importance in our house. it's in the basement. There are books in every single room in our house, however, so I figure this shows them where we think the real importance lies....
My point: let them find the balance themselves. One of the benefits of homeschooling is that there are more hours in the day, so spending 2 watching TV, or two playing computer games, isn't that big of a deal. There are still lots of hours to read books, do art, make things, be imaginative, etc. In fact, my 5 year old spends at least 2 hours a day reading.. I don't tell her to read, she just does it..... And my son with his own phone? He only asks to play it about once a week. He'd rather be playing Rescue Hero's with his toys or outside in our yard, with his fire truck and police car (his bike). And yesterday, while waiting for dinner, he asked to play Starfall for the first time in weeks....
The author of the Atlantic Article put her Ipad in her toddler's toy bin. He ended up treating it just like any other toy. I;ve found this to be true in my kids' experience, so when they ask to play on a tablet or on the computer, I usually say yes. They don't ask all that often, it's become like any other toy in the house, something they enjoy for a while, then get bored with, then enjoy again, etc. My daughter ignored her tablet for over a month, but in the last few weeks has rediscovered it and is addicted to playing My Little Pony.
It's all just stuff to use, and if you let their interest guide the use, you will find that media stuff just becomes one more option, not something to "plug in to" for days on end.