The Boys' Guide to Growing Up and The Girls' Guide to Growing Up. The books are written at a Grade 3 level with illustrations and the information is clear and positive.
They're targeted to youth with intellectual disabilities but I think are great "Coles Notes" versions for any pre-teen or teen -- cutting through jargon and delivering the facts kids need to know.
The boys' guide includes everything from what to do about zits and body odour to crushes, masturbation, keeping yourself safe and what's private and what's public.
The books are written by a sex educator who has a daughter with Down syndrome.