There is (I know from my sister-in-law’s family trip) a Harry Potter world thing out there too and as my 6.5 yr old daughter is massively into HP this may be something that matters.
What I will say is that a week is a short amount of time when you’re also dealing with all that jetlag. Like having done back to the UK and out to Aus twice in a few years it’s definitely extra tough with a kid that age. She took at least 4 days each time to adjust. I was about the same because of her. When you’re on your own you can just sort of power through, drink to excess or whatever.
So you’re taking the older kid I’d look at a longer break if you can (I realise that is tricky as you probably only have half-term) but also don’t forget when you get them back again you’ll be in the same situation in reverse.