I've registered my daugther in the site called Carrot Sticks. It's a site where children can practice their maths online. It's quite exciting since they earn points for every correct answer they give and they also get a chance to challenge another player who's online. One thing I also like with the site is that they can't chat with their opponent which I think makes the it safer for the kids and avoid unnecessary chatting.
I like how the internet has a lot of useful tools for education like they have online maths online accounting, online spelling and etc . But I also try to be more careful with the kids use with the internet.