I think the kids are wearing clothes they’ve been photographed in before, for the outward and return journey quite deliberately, so that the photos look the same as ones taken previously, so have less value.
George wore thé Hennés t shirt and shorts for the regatta thing andCharlotte the tartan dress for her birthday portrait.
A listers who don’t to be photographed wear the same boring clothes ( eg Madonna in tracksuits when she lived in London) and probably Kate in her skinny jeans and Breton tops.
It’s the Z listers who change their clothes 10 times a day, in the hope that they’re papped.