Thanks to all who generously sent thoughts.
I asked around more broadly elsewhere, generating the following list of options.
Sub-3.0 High-wind adult-focused sails: Northwave Surflite (2.3, 2.5, 2.8)
northwavesails.com/surflite/ Sailworks Revolution (there's a new 2.5)
www.sailworks.com/the-gear/sails/2021-sails/revolution.html Duotone Now (2.4, 2.8)
www.duotonesports.com/windsurfing/sails/now/ Goya Fringe Pro and Fringe X Pro (2.8)
goyawindsurfing.com/sails/y2020/fringe-pro/ Sub-3.0 High-wind adult sails designed for foils: Teivasails Swart (1.5, 2.0, 2.5)
www.teivasails.fr/windfoil/?utm_source=seabreeze.com.au Sub-3.0 youth sails with apparent adult high-wind foiling potential: Severne Redback and XS-3
www.severnesails.com/sails/redback/ Sailworks Ripper
www.sailworks.com/the-gear/sails/2021-sails/ripper.html Goya Scion
goyawindsurfing.com/sails/y2020/scion-x-pro/ Hotsails Micro-KS3
www.hotsailsmaui.com/tech/microks3/ Patrik 3-Micro
patrik-windsurf.com/sails/ Actual testimonials were scant, though:
The sub-3.0 adult sails above are mostly pretty well-known, and have been widely used on foils.
No one offered first-hand experience with the Teiva foil-specific tiny sails.
Many expressed curiosity about kids' sails for high-wind foiling, but only three first-hand experiences materialized.
1. Several love their Hot KS3s so much they're sure, without actual evidence yet, that Micro-KS3s will be similarly awesome.
2. My kid, when small, learned to windsurf on Sailworks Rippers, including ripping the Gorge in 20-25 kts and planing through jibes. Despite low tension, the Rippers, especially the 2.5, exhibit impressive dynamic response under load, much like stable, tuned adult sails. I think they're promising for adult high-wind foiling, but haven't actually tried them (cause ours are now mast-less).
3. There's one actual solid piece of testimony. One of the Columbia Gorge's best foilers, a Goya team-rider usually on Fringes, sometimes gets blown in 25+ onto a Scion 2.5 youth sail-which fact is only evident to onlookers if you look at the writing on the sail. So despite its fairly straight luff curve, the Scion clearly works well in gusty high wind.
By the way, a few noted that for riders taller than 160 cm, the low boom cut-outs of youth sails can be an issue.
Apart from that, there appears to be high-wind potential in stealing from your kids.
Thanks to all who replied.
Evan Goldstein
Seattle, USA