Husband has glioblastoma - how to deal with children?

My husband was diagnosed in June with glioblastoma, grade IV. He's had surgery. They removed about 65%. He is currently undergoing radiation and chemotherapy with Temodor. He's 39. The tumor is in his cerebellum. We found out about the diagnosis because he started having a tick in his hand where he couldn't stop his hand shaking. I never would have imagnied that was due to a brain tumor. We have two young girls ages 6 and 10. They know he was in the hospital and had brain surgery for a tumour. They don't know about the bad prognosis. We're hopeful that he can beat this--or at least for several years to come. But, the girls see him sick and tired on the couch, or doubled over as he walks. I'm not sure how much I should be talking about what is going on with him. Or preparing them for the worst case scenario? Anyone else have any stories about glioblastoma in a family with young children?

Thanks,

Kelly