Unexpected Findings About Kids Feet

Over a period of several months in 2026, Aetrex foot scanners captured millions of individual foot scans across thousands of retail locations spanning multiple countries and retail partners across running specialty, multi-sport, and general footwear environments. Every scan was generated by the Albert2 scanner, which uses structured light and 3D reconstruction to capture sixteen distinct measurements per foot — producing a clinically precise three-dimensional model of both feet simultaneously. Aetrex is sharing these findings to advance the industry conversation around fit, last design, and how footwear is meeting — or missing — the needs of real customers. This is the second in a series of insights. Today’s focus: children’s foot development and where the sizing system breaks down.

Key Findings Below

1. The arch inflection at age 6 should be a product design threshold.

Children under 6 have developmentally flat arches that are normal and self-correcting. Shoes with rigid arch support in this age group may interfere with natural development. Product lines and orthotic recommendations should differentiate below and above age 6 — this dataset provides the biometric evidence to justify that distinction at population scale.

2. Children’s footwear needs a width strategy, not a single standard.

The three foot profiles identified in this dataset — mid-size typical (219.7mm, 91.3mm wide), large wide-footed (239.7mm, 115.4mm wide), and small narrow-footed (171.5mm, 78.1mm wide) — span a 37mm range in foot width. A single standard last cannot meaningfully serve all three. Children’s footwear ranges that do not account for this structural variation are, by default, fitting the majority of kids poorly.

3. Gender-differentiated kids’ lines are not supported by the scan data.

Age and foot size explain virtually all of the variation in children’s foot profiles. Gender does not. A boy’s foot and a girl’s foot of the same age and size are biometrically indistinguishable. Product design and recommendation systems that differentiate by gender before age 12 are adding complexity without biometric justification.

4. Children’s bilateral asymmetry is higher than adults — and already measurable.

A 6.0 mm mean left-right difference in children means that fitting from a single foot measurement is even less reliable in kids than in adults. The scanner already captures both feet simultaneously. Surfacing this asymmetry at the point of sale for children’s footwear is one of the most direct improvements a retail partner can make today.

Growth Is Linear — Sizing Should Follow

Of the scans in this dataset, tens of thousands belong to children — scanned across the full age range from toddler to pre-teen. The single most important finding about children’s feet is also the most actionable: foot growth is highly predictable, and shoe sizing should be able to track it almost exactly. It doesn’t.

Foot length grows linearly — 164 mm at age 2, growing at 7.7 mm per year to reach 241 mm by age 12. This predictability is the good news. The EU shoe size system tracks foot length almost perfectly (r=0.95), meaning the sizing scale itself is well-calibrated to growth. The problem is not the scale; it is the shape assumptions baked into the shoes at every point on that scale.

Unlike adults, where gender is the dominant organizing force in foot shape, children’s foot profiles are driven by age and size — not gender. When advanced pattern-recognition is applied across all 15 biometric features simultaneously, gender ranks near the bottom as a differentiating factor. A boy’s foot and a girl’s foot of the same age and length are essentially the same foot. This has direct implications for product design: gender-differentiated kids’ lines are not supported by the biometric data.

The Arch Inflection at Age 6: A Developmental Threshold That Changes Everything

The most clinically significant finding in the entire children’s dataset is a single, sharp transition at age 6 — the point at which the arch ligament begins forming in earnest.

The ArchDepth score — a continuous measure of arch development captured by the Albert2 scanner — sits near zero for virtually all children under age 6. At age 6, it jumps sharply to approximately 7.7, and continues rising through childhood. This is not noise in the data; it is the developmental inflection point documented in pediatric literature, now visible at population scale across tens of thousands of scans.

Flat arches in children under age 6 are biologically normal and require no intervention. The arch ligament has not yet ossified. Orthotics and rigid arch support in this age group may actually interfere with natural development. After age 8, however, a flat arch that has not begun to develop warrants clinical attention — and this dataset can identify exactly which children fall into that category at the point of purchase.

The retail implication is stark: a shoe with a built-in arch support is appropriate for a 9-year-old and potentially harmful for a 4-year-old — yet many children’s footwear lines apply the same last across the full age range.

Three Distinct Children’s Foot Profiles

When the children’s dataset is analyzed across all biometric dimensions simultaneously, three consistent and biologically meaningful foot profiles emerge — each representing a genuinely different shape, defined by foot length, arch development, and heel geometry, that requires different footwear.

The most important nuance is the contrast between the large wide-footed and the small narrow-footed profiles. The large wide-footed group (21% of children) has a relatively low Arch Depth score of 4.6, suggesting a wide foot that has not yet developed strong arch definition. Standard wide-fit children’s lasts, which often include arch support, may be geometrically inappropriate for this group at younger ages. The small narrow-footed profile (mean age 5 years) presents a virtually flat arch — consistent with developmental stage, not pathology — and needs a narrow last that the market largely does not offer.

Arch Development by Age: The Data That Retail Ignores

The arch depth score progression across age groups is one of the clearest developmental signals in this dataset. It has direct implications for when arch support is appropriate — and when it is not.

60% of all children in this dataset score 0–3 on the ArchDepth scale, confirming that arch formation is genuinely still in progress for the majority of scanned children. The question is whether the footwear on a child’s feet during that process is helping or hindering.

Left-Right Asymmetry: Worse in Children Than Adults

Children’s feet are more asymmetric than adult feet — a finding that compounds the already challenging fit picture.

The mean bilateral asymmetry of 6.0 mm in children versus 3.9 mm in adults suggests that left-right differences are not just larger in childhood — they are a normal part of development. Children’s feet are still finding their final shape, and that process does not unfold symmetrically. Recommending a single shoe size for a child without measuring both feet is, by default, fitting the wrong foot.

Key Findings at a Glance