As regards the bereavement and funeral trauma, which I do not in anyway underestimate, none the less other children have childhood bereavements and difficult funeral experiences in their lives, albeit not in the public eye.
In my case my father committed suicide when I was seven. My parents had divorced and Mum remarried when I was a baby and I had a very happy childhood with my stepfather being basically my father. However I am the youngest, so my older sisters had a different experience and were obviously closer to my father and saw more of him than I did.
On the day he died I remember Mum breaking the news to us and one of my sisters asking how he had died and a being told he had a heart attack. It wasn't until I was an adult with questions that I obtained his death certificate and discovered it was suicide and let my sisters know. This was never discussed with my mother or step father or other members of the family such as aunts who would have known the truth.
My eldest sister was 15. Daddy had taken her to Germany to drop her off at an exchange family and come home and killed himself. Mum didn't want to disturb my sister's trip so she wasn't told till she came home. None of us were given the opportunity to attend his funeral. I have no idea where he is buried though I do sometimes consider tracking it down to visit. Not really sure where to begin finding out - key people who would know are either dead or past remembering.
Anyway, I think my eldest sister definitely has grounds for long term trauma and resentment but she has lived a happy life bearing no particular grudge against our mother (beyond the tricky relationship we all had with her as she was a somewhat difficult personality).
In fact she had this weird thing about death. She just couldn't discuss it. Ever. As a child one would come home from school and look for the dog/hamster/pony and they would be gone. She'd have them put down (when they needed it obv) but never discuss it with us.
My next sister up spent a year in Switzerland as an au pair. When she came home we had a sweepstakes laying bets on how long it would be before she had a row with Mum. We were all over generous with our time estimates. The first thing she said when we met at the airport was "I can't wait to ride (her favourite horse)" and Mum replied "I'm so sorry, she broke a leg and had to be shot" prompting a massive row starting in arrivals! Of course the poor horse had died many months before but Mum wouldn't have her told as it would make her homesick apparently.
Anyway I tell you all this by way of offering a different experience of death of a parent and a family dealing with it. Of course the secrets couldn't have been kept if we were a family in the public eye. I don't think any of us particularly carry childhood scars as a result though it might mean we have parented our own children differently.
Harry's experience is unique to him. His perspective different to William's as W was older and had been party to much more information than H would have been exposed to. I don't doubt the trauma and shock he suffered. But many other children have traumatic experiences, also unique to them, and while they may be blessed in not having to deal with it in the public eye, I don't think it gives H a unique pass to bitterness and blame. He needs to put it all behind him as so many other children do.
I often think about children whose father's murdered their mother. That must be an appalling trauma to get over, and effectively losing both parents not one. I've not looked at studies or statistics if they exist but I'm sure some go off the rails and never recover and others gratefully accept the anonymity that comes with time and public forgetfulness and get on with their lives. Harry needs to get on with his.
I'm also pretty sure I remember when H & W did an interview/tv program celebrating their Mother's life (?2017 twenty years anniversary) when they said they wouldn't be discussing her publicly after that. Obviously some things like the Bashir scandal have meant they couldn't ever not mention her again but I thought there was a general intention to treasure their own private memories of her and not go on revisiting her death (publicly) every year.
Perhaps Diana and her death will occupy a relatively small chunk of the book. I hope so.