So I'm not great fan of the Middletons but I thought their presence was practical and handled very well. My guess is that Nanny Maria was off with Louis (rumor has it they were their just somewhere private) which is logical since a 15 month old on a boat can be a recipe for disaster and/or tantrums. Michael and Carole watching the older kids was the most logical solution to allow George and Charlotte to participate and still have proper supervision.
Now where I have an unpopular opinion is with Charlotte's sass. Last year her sass towards RRs at Louis christening was excused because she was 3, RRs are meanie heads, and of course W&K told her off in private. This year the sticky out her tongue at someone when instructed to wave is being excused because she's only 4, she was probably told to wave at a friend (or William) so that's just cute, if not waving at a friend then RRs/Paps must have been sticking their tongues out at her to get a reaction (like they did to her father and uncle when they were kids), and of course Kate told her off in private and how dare you expect her to do so in public.
Of course I understand that any parental action would have been widely reported and judged to high heaven but look at how two sass events 13 months apart a being completely excused. They very same behavior by a 6 or 8 year old would have caused horrible parents and bratty child responses. At what age does cute sass become brat? And is this something we will look back on a say was the start of Charlotte the brat?
I could be very wrong but those are just my thoughts. Charlotte is one of several that I'm watching for the switch from cute sass to brat. Spunky and sassy is generally fine but gentle correction will teach Charlotte how to behave in public. Yes she's only 4 and we don't want them to crush her spirit (and of course correcting in public is not the best idea) but my worrywart senses have been activated.
Sorry for the length.