I've just watched their recent "school" shopping vid and they seemed to get nowhere near enough stuff for Sienna to be able to learn to an appropriate level! I've watched another video of school supply shopping for homeschooling and they got so much more to enable their kids to learn to their best ability.
Obviously they may already have stuff like pencils, rubbers, rulers, pencil sharpener for example but I don't see one notebook as sufficient for a years worth of learning spanning a range of subject areas.
If I'm correct (which I think I am) Sienna would be going into yr6 a.k.a SATs year meaning her peers would know at least basic mental and written maths as well as spelling, punctuation, and grammar. We were rarely allowed to use calculators at that age because it was about building basics. Sienna seems to be able to read but how much can she actually comprehend because understanding what you're reading is just as important as being able to read at that age. Do Georgie and Darren ever actually ask her questions about what she has been reading? Does Sienna feel comfortable asking or finding out meaning of words and phrases she doesn't understand? Do they sit with her and work through things or just leave her to her own devices?
Darren and Georgie at the very least you need to sit with her and ask her questions, do some maths about money cos that's something she'll definitely use in the future, and teacher her basic grammar/punctuation cos online editors/autocorrect can only help when you're at least somewhat close to it being correct!