Salam! Good question. Brotherhood of the Wolf does have violence and scary moments. That said an 'alim (Ustadh Anwar Mangal) who read chapter 0 of our series and has had his children read it, said this about our series to a parent with an 8 year old:
"Might be a little complex for an 8 (plus a little amount of gore too, although nothing more than what they already see in video games), but then maybe your 8 is an avid reader."
So, my recommendation would be to read it yourself before handing it to kids, tbh.