Almost everything that makes colouring feel good or feel like work comes down to one property: how hard you have to press.
Soft cores, not colour count
A soft core lays down pigment with almost no pressure, so colour goes on evenly, layers blend, and your hand does not ache after twenty minutes. A hard core needs force, which makes flat colour patchy, tears at the paper and turns a wind-down activity into effort. This one property is most of the price difference and none of the marketing.
Twenty-four is the sweet spot
Beyond that you are buying shades you could mix by layering, and very large sets tend to be large instead of good. If a set has seventy-two pencils at the price of a twenty-four, the saving came out of the core.
The centred-core test
Look at the sharpened end. If the coloured core sits off-centre, the pencil will snap repeatedly no matter how carefully you sharpen it, and no price protects you from this — it is a manufacturing tolerance, and cheap sets fail it constantly.
For children, buy cheap deliberately
The real cost of a child’s pencils is not quality, it is that eleven of them will be lost by March and two will be found in a washing machine. Buy an inexpensive soft-core set, expect to replace it, and spend the money you saved on paper instead.