I appreciate that Isla set the standard on kids bikes, and if you can afford a new one or a second one, good on you. I understand that people only lose £60-£80 in depreciation from the examples above.
Both my kids started on second hand Ridgebacks, Treks, Spesh and Carreras, many found on here! Never paid more than £100, all got ridden and well used, often by both kids, never lost more than £40 – £10 per year – when selling them on.
Just depends if you can afford the original cost. (My youngest now on a Frog btw, as MrsMC decided we could afford it. Eldest on an Inbred and coveting my Soul now he is my height 🙄 )