Taita Discovery Centre: Near Tsavo West National Park; has structured and tailored courses; also takes conservation-focused gap year volunteers http://www.aboriginal-ecotourism.org/spip.php?article291. Link with other parks / parts of the country through this (unvetted) tour company
Kenya Voluntary & Community Development Project: medium to long term gap year, and 3-4 week voluntours that take (accompanied) children. Frommers rec as well.
Inter-Community Development Involvement affiliated with University of Indiana; takes medium term gap year in AIDs and education work; registered US 501(c)3. Frommers rec as well.
Responsible Travel: starting point for finding tour operators; see family tailored safari & cultural tour
Eco-Resorts - Cultural tours, including homestays, and short trem family volunteering in Mura Masai region. Frommers rec as well.
IntoAfrica - "Fair-trade" and locally-based cultural trips; customized departures for groups as small as 5
Origins Safaris - Cultural tours. The 7-day conservation and 14-day education projects both look fabulous, though breathtakingly expensive.
Through Pack for a Purpose:
Deloraine Lodge: Great Rift Valley - affiliated elementary school. Lodge also organizes horseback safaris, though I don't think our riding abilities would be sufficient
Kicheche Bush Camps - Affiliated with London-based non-profit as well as PfaP; several locations; supports several schools and health clinics. Somewhat troubling, repeated emphasis on how little they value "rigid" scheduling...
Ol Donyo Lodge: Outpost for Ride Kenya Safaris (also, sadly, almost certainly beyond our riding ability); affiliated with two schools
Through Pack for a Purpose:
Deloraine Lodge: Great Rift Valley - affiliated elementary school. Lodge also organizes horseback safaris, though I don't think our riding abilities would be sufficient
Kicheche Bush Camps - Affiliated with London-based non-profit as well as PfaP; several locations; supports several schools and health clinics. Somewhat troubling, repeated emphasis on how little they value "rigid" scheduling...
Ol Donyo Lodge: Outpost for Ride Kenya Safaris (also, sadly, almost certainly beyond our riding ability); affiliated with two schools
Frommers Picks:
Lewa Wildlife Conservancy - Local NGO focused on conservation broadly defined; has some sort of accreditation system for "green" lodging and campsites; also supports wide range of community and education projects. LWC links to Pack for a Purpose, but only two of LWC's very long list of projects appear to be included in PfaP's programs. Frommers rec. as a starting place for finding volunteer placements; less clear how to use it this way but it *does* seem to be a possible vetting for lodging that's not top-top-end luxe.
Note: Generally Frommers is my go-to guide; in Africa (and Kenya in particular) they seem mostly just to rephrase and rehash Lonely Planet content.