I don't know their ages, but Rusty & Rosy is great for younger students. There is a separate hard drive and the kids are not on the Internet while learning.

Have you tried NetNanny, which allows parents to restrict Internet access? This would allow the kids to study online with restricted access to other sites.

NetNanny

Rusty & Rosy

Good luck!

Daa'iyah Na'im
Director/Head of School
The AGVI Academy for Gifted Youth
http://AGVIgifted.org