Child SSI structurally absent: ages 0–14 have no disability signal (baseline child SSI 0.12M vs SSA 0.98M); seed qualifying disability per the #430 pattern

Summary

Child SSI is structurally unrepresentable on the certified default: ages 0–14 carry zero disability signal (the CPS ASEC disability battery starts at 15), so is_ssi_disabled can never fire for them. Measured on Build M (98bf731, bundle 4.21.1, pe-us 1.764.6, TY2026):

The #430 take-up banding lands both adult groups within ~2% of SSA — the entire remaining baseline gap (~0.86M) is the missing children. The 0.12M we do produce are 15–17-year-olds (is_disabled = 7.1% weighted at 15–17, 0.00% at 0–14, 11.4% at 18–64, 25.3% at 65+).

Downstream effect

Any SSI reform scores ~zero child impact. For the resource-limit class (#374 thread): CBPP's published Table 1 has 23k new child beneficiaries under $10k/$20k and 49k under elimination; our CBPP age bridge reports 0 in every vintage. Child SSI eligibility runs through parental deeming (the parents' countable resources are what the asset limit tests), so with the SCF asset columns now present, disabled children are the only missing ingredient — the reform mechanics would work immediately.

Suggested fix

Seed child SSI-qualifying disability for ages 0–14, banded to SSA's child caseload by age (~0.98M under-18 recipients), following the #430 take-up-banding pattern — i.e., assign qualifying-disability flags so that simulated child SSI (through deeming + the seeded take-up contract) hits the admin totals. On ACS-spine lineages (#403), the ACS PUMS disability items (asked from age 5) can inform the assignment directly rather than a pure random seed.

Relates #430 (pattern), #374 (CBPP child rows), #361 (input surface), #403 (multispine). Found while benchmarking the certified default against CBPP/SSA for the SSI resource-limit analysis.

Read the #430 take-up-banding pattern and trace the child SSI eligibility and parental-deeming path first. Then inspect the ACS PUMS disability items on #403 lineages and the available SCF asset columns. Done means ages 0–14 receive qualifying disability signals, simulated child SSI aligns with the SSA child caseload, and the CBPP child rows no longer report zero.