Great thread going here. My two cents. First, a few links. For those interested in language acquisition (OPOL, mL@H, etc.), check out the Multilingual Children’s Association. You could spend the better part of a day in there reading just the links off the FAQs. And yes, they have a discussion forum. Second, a PDF file of Laura-Ann Petitto and Kevin Dunbar’s recent findings in educational neuroscience on the subject of bilingual brains (the first nine pages are relevant). Here are the summary paragraphs regarding previous and new findings:
[quote] We found that (1) early (before age 5) bilingual language exposure is optimal for dual language development and dual language mastery (Kovelman & Petitto, 2002). (2) Those bilingual children who are first raised monolingual from birth and who are then exposed to a new language between ages 2-9 years of age can achieve the morphological and syntactic fundamentals of the new language within their first year of exposure. However, this rapid acquisition of new language fundamentals is possible only when extensive and systematic exposure to the new language occurs across multiple contexts, for example, in the community and home, with far less optimal dual language mastery being achieved if exposure comes exclusively within the classroom (Kovelman & Petitto, 2003; Petitto, Kovelman & Harasymowicz, 2003). (3) Bilingual children exposed to two languages from birth achieve their linguistic milestones in each of their languages at the same time and, crucially, at the same time as monolinguals (Holowka, Brosseau-Lapré & Petitto, 2002; Kovelman & Petitto, 2002; Petitto & Kovelman, 2003; Petitto, Katerelos, et al., 2001). (4) Bilingual children exposed to their new language between ages 2-9 years of age exhibit “stage-like” language development in their new language. Surprisingly, this stage-like development is highly comparable in content to the stagelike language development typical of monolingual children acquiring the language from birth, differing of course in the age when it occurs given the later exposure to the child’s other language (Kovelman & Petitto, 2003). (5) Importantly, introduction of the new language does not ‘damage’ or ‘contaminate’ the home language of the child (Petitto et al., 2003).
In both behavioral and brain-imaging studies, we found that the age of bilingual language exposure has a significant impact on children’s dual language mastery. Remarkably, early age bilingual exposure has a positive impact on multiple aspects of a child’s development: linguistic, cognitive, and reading. Children who experience early, extensive, and systematic exposure to both of their languages quickly grasp the fundamentals of both of their languages and in a manner virtually identical to that of monolingual language learners. As adults, these bilingual individuals, in addition to their good behavioral performance on language tasks, also show that their brains are processing their two languages in a similar manner, and virtually identical to monolingual adults. The field raised concerns that early bilinguals may be linguistically, cognitively and academically disadvantaged. Our findings suggest that early bilingualism offers no disadvantages; on the contrary, young bilinguals may be afforded a linguistic and a cognitive advantage. Early dual language exposure is also key to skilled reading acquisition. Moreover, learning to read in two languages may afford an advantage to children from monolingual homes in key phoneme awareness skills vital to reading success.[/quote]
For what it’s worth, I think it’s far more interesting to hear what’s in this thread and others like it – research is great and all, but there’s nothing quite like real world experience. To wit, in case you missed them, some of the older Forumosa threads on children and language acquisition are [url=Does Your Kid Spontaneously Translate? [url=What language does mama speak? [url=Immersion experiences with young kids (2 & 4)? and [url=Is Mandarin taught in your home? 
But on to eloquence. Here’s what the OED has to say on the matter (slightly different from the Wiki def):
BTW, there’s a rare usage of the word that denotes a group of lawyers – “an eloquence of lawyers.”
As pointed out several times on this thread, eloquence is rare even in one language. Eloquence would seem to involve familiarity with many rhetorical conventions and strategies, a rather sizable vocabulary and attendant proficiency in word choice, outstanding public speaking and composition skills, and a propensity for metaphor verging on the poetic. In Chinese, imagine a speaker trying to convince an audience of something – speaking with great power, then dropping precisely the right proverb at just the right moment during the speech - with the result that the hearers do mental oohs and ahhs. In English, listen to Martin Luther King, Jr.'s “I Have a Dream” - or read “Letter from a Birmingham Jail.” And then there’s always Plato-cum-Socrates doing the dialectic two-step with his interlocutors, esp. in the Phaedrus.
So are we really talking about eloquence here? Or is it a matter of “Which language would I like my child to be more / highly proficient in?” And the deeper question, which sjcma raised in relating the immigrant experience, “Does part of this stem from my fear that my child will become local, i.e. foreign to me?” Whereas many immigrant parents try to prevent their children from becoming “too local,” the children usually become bilingual and bicultural to a far greater degree than the parents ever did (or ever wanted). Chaos theory meets language acquisition in the margins of culture. While I’m not presuming to answer these questions, IMHO, parenting involves regularly questioning your own motives while being flexible enough to refigure goals and expectations along the way.
In this household, we’re OPOL, and it works well for us. Smell the Mitten has no problem speaking English to me and my folks, Chinese to Smell the Wife, and Taiwanese to the babysitter. Of course she mixes – perfectly natural, and when she learns the appropriate word or phrase, she swaps it in – happens all the time. Does she get 30% of her waking hours in the minority language? Definitely. And her little brother hears English from me constantly – only two months old but he always smiles when I say “hello.” As for forcefulness, vocabulary, rhetorical skill, critical thinking, public speaking, and expressive/persuasive writing, well, down the line and if I’m still alive, we’ll see. Verbal/linguistic isn’t the only intelligence, even though it and logical-mathematical still have quite a bit of currency in traditional education systems and mindsets. As for right now, I believe I have successfully fostered a love of reading (story time every single night, monthly trips to Taipei Public for more books, her own little bookcase) and she’s starting to read a bit on her own (been doing about ten minutes a day on phonics for the past year), but that could go anywhere, and most of the time, well, we just play.
Eloquence as a parenting objective? Nothing wrong with that - cognitive (reasoning) skill and affective (emotional) expressiveness are worthy objectives in any language. As Maoman pointed out, there are indeed children whose parents want them to be concert pianists, doctors, etc., and children who go on to fulfill their parents’ dreams (which, in some cases, coincide with their own).
So what steps to take for eloquence? As your daughter grows up, you could encourage her to become active in speech and forensics and acting, learn lots of words and practice discriminating in their usage, practice writing in all forms (particularly persuasive essays, which you will definitely want to submit to various places since eloquence is always an audience value judgment), and read extensively (probably wouldn’t do to have her speaking the way James Joyce wrote, though). Sounds like a lot of work – and it’s worth keeping in mind that unrealistic / rigid parental expectations have alienated many a child. But offered as a possible direction, well, she might just go for it and one day put us all to shame. Not that we were ever all that good to begin with. 