Highchair tip-overs follow from geometry rather than from build quality. A chair that stands solidly when empty can be unstable under the forces a toddler actually applies.
Stability depends on the base footprint
An object stays upright while its centre of mass remains above the area enclosed by its supports. Tipping begins when that line passes outside the footprint.
A highchair carries a seated child well above the floor, so the centre of mass is high. A high mass over a small base has very little angular margin.
Widening the base at floor level is the most effective single change, which is why stable designs splay outward rather than dropping straight down.
Pushing against a table is the usual trigger
A child pressing their feet against a table edge applies a horizontal force at height. This is the most efficient way to rotate the chair backward.
The force involved is well within what a toddler can produce, and it is applied deliberately and repeatedly once the effect is discovered.
Positioning the chair so feet cannot reach a fixed surface removes the mechanism rather than relying on the chair to resist it.
Height adjustment changes the calculation
Adjustable chairs raise the seat while keeping the same base. Every increment raises the centre of mass and reduces the margin before tipping.
Reclining functions have a similar effect by shifting mass backward, particularly with an active child leaning further in the same direction.
Folding designs introduce joints that must lock reliably. A partly engaged lock can hold under static weight and release under a sudden shift.
Restraints address a different failure
A crotch post and harness stop a child sliding down and under the tray, which is a separate hazard from tipping and one that trays alone do not prevent.
A tray is not a restraint. Children can stand on the footrest and lever themselves up over it, and the tray can detach if used to take load.
Five-point harnesses restrain the torso as well as the waist, which matters because a standing attempt begins with the upper body.
Where standards stop and placement begins
Product standards include stability tests using defined loads and forces, and a compliant chair has passed them under those conditions.
Real use includes forces the test does not model, including siblings pulling on the chair and floors that are uneven or slippery.
Positioning away from walls and table edges, keeping the harness fastened and following the manufacturer's instructions for the specific model do more than any comparison between compliant products.