Our story is told by the adult version of the boy who experiences all of the book's strange occurrences at the age of seven. So we are able to experience the story as it happens, with the occasional added insight of someone who has had years to process all that happens. Check this passage out as an example:
I watched as my father's free hand, the one not holding my sister, went down and rested, casually, proprietarily, on the swell of Ursula Monkton's midi skirted bottom. I would react differently to that now. At the time, I do not believe I thought anything of it at all. I was seven. (7.24)
On the other hand, he's telling the story decades after it happened, so sometimes details that we wish were clearer are a little bit vague or fuzzy—and it doesn't help that his memory was pretty much wiped by Ginnie Hempstock, either. But it's a compelling way to tell a story, that's for sure.