The future isn't a static. What I mean by that is, what's going to happen isn't set in stone. It may be that god sees the past, present and future as a web, with many different paths. He sees all possibilities that could happen, but we humans actually pick the path through our free will.
Yes, he likely knew that them eating of the fruit was one of the possibilities. However, he also likely knew what would had happened if they had took the path where they didn't eat of it.
Compare it to this. A scientist with a maze full of rats. The scientist has a panoramic view of the entire maze. Where each path leads. Some lead to a dead end, while others lead to the prize. We are the rats, god is the scientist.
This is all assuming that god exits, which is a question I feel that most people don't have an answer for.
What if at the same time there exists a reality where they did not eat the fruit?
Adding multiple worlds theory to this makes it quite interesting philosophically.
Then it is no longer a question of "how did God not know they would disobey" and more of "what is to be gained from permuatations of creation with differing outcomes." ---