Be honest. One of my little girl's best friends died of brain tumour at 5yrs old, and if it is the same type of tumour, the prognosis is devastating. At 7, your little one will understand facts, and I would urge you not to give false hope. With my little girl, I made sure to reiterate that doctors were trying to help her feel better, rather than make her better, as we knew that the diagnosis was terminal from day 1. Children are very factual, and much more accepting than we as adults. We know the horror of what the child and her family are enduring, and how wrongly is, in the natural order of things, whereas a child will often accept the facts, feel sad, but not realise the true awfulness of the situation. For example, my daughter barely batted an eyelid when she saw her friend in a wheelchair for the first time. I was always very careful to mention, every time we discussed her friend, th at her illness was rare, and that not many people get ill like that etc. But I never told her that doctors would make her friend better, as this may have affected her trust in me, if she thought I'd been dishonest.
Utilise the school elsa, if you feel you need to- they did some great work with my daughter when her friend died.
Simon Says and Winstons Wish have some good advice on their websites.
Be kind to yourself, telling my daughter, and helping her through that period was the worst thing I've ever done in my life. But 15months on, and she is doing amazingly, talks about her happy memories with her friend, enjoys visiting places we went together. Thoughts are with you. xxX