I don't know much about the baby part, but I found this a long time ago(however, it is formal stuff, check out the "Learn" section). Kids Web Japan

Also, for kanji learning, you WILL need to use this in conjunction with other kanji learning material, first of all, because this doesn't present you with all definitions for each kanji(at most, they only have one or two definitions), and second of all, because it only has up to the sixth grade. Here is the site: https://www.msu.edu/~lakejess/kanjigame.html

I recommend Tuttle's A Guide to Reading and Writing Japanese, because it includes all the definitions, on-yomi and kun-yomi readings, a few compounds, plus the stroke order and all kanji needed for complete literacy(the only kanji they don't go into are the kanji that the Japan Newspaper Association added for use in newspapers). I love this book. Finally, maybe LiveMocha can help a wee bit Language Learning with Livemocha | Learn a Language Online - Free!. I hope some of this helps.

Either hire a nanny who is Japanese native and instruct him/her to only speak Japanese full time to the baby or don't do it. Babies don't learn languages like adults, they just do the monkey-see-monkey-do thing which makes them learn much much quicker but only if the carer is 100% fluent.

2 years of Japanese tuition is not enough for fluency. Any mistakes you make (and you will make lots), the baby will pick it up and commit to memory and it would be very hard to correct later.

That seems to be the popular opinion, so let me try to reframe the questions.

Would watching Japanese children's programming, like PythagoraSwitch, be beneficial to my nephew?

Which level JLPT would I need to complete to be considered competent to speak Japanese to a baby?

Steven

If you're doing it according to the JLPT, you will most likely only be able to speak formal Japanese, which is fine, because of the politeness, however, according to a fairly large amount of people, if you are really familiar with a Japanese person, they get offended if you use polite Japanese. In other words, there are two types of Japanese; formal, which is more likely than not the one that will be used more often, therefore is taught most, and informal Japanese, which is used amongst close friends and unfortunately in most anime, which means that watching anime for the purpose of learning Japanese is really not the way to go, although I would imagine that the stuff made to educate kids would be different.

I agree with kirakira; hire someone that can speak fluent Japanese to take care of the kid, and you may also learn a fair amount of things as well. Also, you should probably go to a university that teaches the language so that you can learn it to where you can pass the JLPT 1 test, but remember that they call it "almost native level", because of the two different types of Japanese, and the informal stuff can only really be learned through speaking with the people from whence the language came. If you do take a university coarse, the teacher may also be of help regarding teaching the language to a baby.

Without any exposure in daily life? Not very. Plus, we`re talking about a baby. They should not be watching tv AT ALL until 2 or 3, and even then just barely. Don`t believe any of the educational tv hype - it`s never been proven to do anything other than slow development.
Once they are that age, then they might be able to pick up a word or two from things like Inai Inai Baa (Pythagora Switch is aimed at older kids)... But the thing is, without starting knowledge the talking on tv is just going to be background noise. To put it into perspective, try watching some shows in a language you know nothing of (have never studied, know 0 words in) - and see how hard it is to pick up things without confirmation and interaction.

Another good example would be that there are hours of English children`s programming on tv each day in Japan... Undoubtedly with countless children watching it to "pick up" English. Instead, they pick up a handful of words that aren`t pronounced correctly... And that`s if they`re lucky and are good at picking things up like that.

When you no longer think in terms of JLPT would be my answer.
The JLPT isn`t what matters when it comes to teaching the language to someone from scratch. You can be a horrible speaker, not be able to scrape a decent sentence together, have an appalling accent that native speakers cannot understand at ALL... And still pass the JLPT - possibly all the way up to 1. It measures a very thin slice of knowledge, and hopes that you have the rest. Unless things have changed since I took it, they don`t do a simple test of speaking even for JLPT1.

Not to be a downer, but without being fluent and speaking to the baby and probably with someone else around the baby, you will probably not accomplish much more than Seasame Street did with me and Spanish... 1-10 and water.

If you can, hire a nanny, or send the child to a Japanese language school for kids. But really, if the kid has no Japanese blood, or real reason to learn Japanese, why put them through something like that? I mean if the child enjoys it, it is ok I suppose, but I would not force anything like that on them.

Hahaha. I wonder how people would do here in Norway.. Oddly, the languages are pronounced very similarly.. (Not to say the languages are similar by themselves, obviously, but the "sounds" being used are.) :)