I've had good luck with chamomile and mirtazepine (older antidepressant). That worked REALLY well-- for the short time I took it, NOTHING rattled my cage. It wasn't quite flattening of affect (which it's notorious for) or anyway if it was it wasn't bothersome (actually, after months and months and months of rage, depression, crippling anxiety, and having it all locked inside by a nightmare experience with antipsychotics, it was NICE).
I had a less dramatic effect (at least, in my opinion) with fluoxetine. Other than slight flattening of affect and *ahem* sexual side effects, it didn't bother me. I'm actually seriously thinking about getting back on it-- my anxiety isn't just bothering me, it's upsetting my husband.
I'd probably be as willing to look at benzodiazepines as the older antidepressants. Nasty side effects there-- the benzos might actually be less worse.
Whatever-- If you are going to medicate anxiety, don't treat medication as a total solution. Assuming mental funciton in the normal range anyway, use it for a crutch to mitigate the anxiety until the child can be taught to think his way over, under, around, or through it.
And no, "crutch" isn't a pejorative term. Antidepressants and antianxiety meds are supposed to be crutches. There is NOTHING WRONG with walking with a crutch when you've got a broken leg. Well-- SAME DAMN DIFFERENCE.
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"