This could be a really intriguing piece of writing, but it's badly marred by constant changes of tense. I couldn't read it all the way through because of these, they were pulling me out of the story so badly. You need to make up your mind whether you are writing in the present tense - here and now - or the past tense - he said, I did. Also, please add apostrophes where needed, eg Gram's head, and the thing in a desk that you keep stuff in is a drawer! I'd love to read this again when you've made these changes.
I think you have the makings of a really good children’s story. I love the Raven and idea of a key etc. Personally I think you need to take out a little of the description, maybe bring a bit more of the action into the next chapter. It seems a little busy, could be difficult for the reader, a nine year old, to keep up. Maybe build up more suspense, you could finish the first chapter at, the gate was closed etc. There are some wordy descriptions in the first paragraph e.g. ‘My gaze returned to the night sky, as I peered out at the huge luminescence suspended in the endless inky gloom, my nostrils filled with the piney fresh scent of a passing breeze’ This sounds a bit more like the description an adult book would use. I’m no expert and others may disagree, but I try to get into the head of a nine year old. It’s just an opinion and I hope it helps.