Just because your kids want to play games online does not mean they have to be non educational games. I am amazed at how many online educational games there are out there. I think it is important to check out these on line games as a parent. Play a few, make sure the content of the games are correct. I would like to believe that educational site would have accurate facts but it is always good for parents to check out each site themselves.
My son played a math vocabulary game the other day and I was amazed that there was actually a game for that out there. So if your kid is struggling on a certain subject do a search on games for that subject. You might be amazed at what you find.