I haven’t seen the book, so it’s hard to comment.
In general, I don’t object to young children seeing ‘sexualised images’, though I wouldn’t choose it. It won’t mean anything to them.
I’m in favour of letting children know that life can be very varied, and as long as no actual harm is done, anything goes. I feel that my generation (I’m 83) was brought up to think only one way of life was really acceptable: you got married and had children. Anything else was eccentric at best, wrong or at least sad and pitiable at worst.