Is Charles the most disapointing of the queens children?

Andrew would be the most disappointing, after his recent escapades and his use of the Royal helicopter to play golf, she would be pleased with Charles who has matured with age, but she would be the most proud of Anne for her fantastic equestrian achievements (Olympics, champion of europe plus many other wins) The sports person of the year award, a HGV driver, an expert yachtswoman and at 70 she still carries out more Royal duties and charity work than any other Royal (equal with Charles) .  An altogether fantastic  and well respected Royal Princess.

No. He did his "duty" and produced 2 heirs with blood that is dissimilar enough to be healthy Lads.  The constant inbreeding of the royal family which means they are related to the royalty of Germany & France & Portugal (everybody was a related cousin) which eventually produces bad stock like insane or hemophilia(constant bleeding).  

. I believe Andrew wins that award.  They are showing to be real people, with faults.

No, he is  not. While the Queen may not be happy with all of Charles' actions, they get along just fine after having a sticky patch due to the Dimbleby biography where Charles talked about childhood disappointments,(his mother was just beginning her reign and couldn't see her children as much as she had before).

Charles is the most prepared heir to the throne ever; he takes his royal duties seriously and has been working with his mother in order to learn even more during the last few years. Charles is far from  being a disappointment!

All of the Queen's children sometimes makes mistakes, and she may feel displeasure with their actions, but she loves her children.

Disappointing to who(m)?     It has been said The Queen finds Charles difficult but I think of late, they seem to get along just fine.    But are you asking this re the public, or HM?    All of them, perhaps excepting Edward (?) has had their moments.   More questionable is whether HM has been a good enough mother although juggling motherhood and being Queen has been a hard act.

https://www.purewow.com/news/queen-elizabeth-princ...

Why on earth should he be.

They are all disappointing in their own individual ways. 

Duh. Is the pope Catholic? Is the sky blue?

i would hope not

He has fulfilled his genetic fun­ction of providing an heir so not a complete dis­appointment.

i would hope not