Can you teach sight-singing? I just learned it from experience.

The only actual sight-singing method I know is solfege combined with reading notes and rhythms. Learning to hear the intervals and then reproduce them from written notation is the goal: reading music is a prerequisite. I agree with Kevin: devising your own based on those goals is usually the best way to go, as it can align your abilities with the abilities of the children. Personally, I am a good solfege sight-singer, so I can teach solfege very well, and therefore the children can sing better because of it (I've almost got the 5th grade classes ready to begin sight-singing two-part music). I know some who are not as good with solfege, and can read the notes by following steps and skips without it, generally from experience singing written music, but learning it by rote.

I digress, very egregiously. To answer your question directly: no. However, as a teacher and pedagogue, I would recommend using solfege to teach the children the basic major scale, and then go right into showing them how that would look on the staff (use C major to start for simplicity). Don't emphasize actually knowing the note names at first, just the positions of each syllable on the staff, so they can learn to follow the notes while they are singing. From there, you can transition to other keys when you feel the students are ready. Just show them how the syllables relate to scale degrees.

Solfege and lots of practice.

The choirmaster who taught us solfege used the motto, "Use your brain as a computer, not as a tape recorder." So no rehearsing by rote; we prepared our parts as homework; and wrong notes were discussed in terms of what solfege syllable they should be instead of what we sang, not by banging the right note on a piano. We learned to relate every note to the tonic (doh for major keys and lah for minor ones) and not go note-to-note. And one fine result was singing better in tune, not to mention learning the right notes more quickly and spending less time singing any wrong notes. I think I'd have to find an appropriate drug to help me get through a rote choir rehearsal if I had to do that again. Solfege warmups, a little solfege ditty to solidify the key of a new piece, and a capella rehearsals until the final one, when organ or piano was added.

A good sight-reader is constantly switching between a number of skills/methods: scale-degree awareness, interval recognition, chord awareness, beat awareness. Solfege is sort of the phonics of music-reading: the best tool to get going, but you'll run into music where it's not helpful. And any attempt to teach solfege without at least some music theory is like trying to teach reading without grammar.

But ultimately, something needs to be taught. "Learn as you go" is why sopranos founder on 4ths and 5ths that basses eat for breakfast. But if you're going to "Learn as you go" (and lets face it, most MDs can't MAKE their people take a sight-singing class, even if offered for free), you've got to sprinkle some knowledge in. "OK, 2 flats...so where is DO?" " Let's tune the g minor chord in m. 7." "Basses, you have the 7th, which is why it feels unstable."