Designing for a child carrying water
Water is heavy, and a tank that is comfortable empty can be unpleasant full. The reservoir shape, where it sits against the back, and how the straps distribute that weight are the real design work in this product, and they are the reason the range is built around what a child can carry rather than around the largest tank that will mould.
The shell is blow-moulded, the fittings and mechanism injection-moulded, and the whole thing assembled and checked on site. That matters for a product with a water seal: a leak is an assembly problem as often as a moulding one, and both halves being under one roof is what lets it be found before despatch rather than after.