here's my two cents :-) He's so young right now that I wouldn't worry about learning disabilities until later. Right now he's going to learn what every baby learns - rolling over, socializing with care givers, etc. The American Academy of Pediatrics recommends that babies not watch TV at all until age 2. The more TV young children watch, the less their language skills grow. They need interaction to learn a language.
That being said, what a lucky boy you have! Babies don't learn and retain language from learning from TV and DVD's. But they do learn and retain language from interacting with live people. Your son has a great opportunity to grow up trilingual!!
I'm Caucasian and speak only English. I've dabbled in Spanish and Mandarin Chinese. My son's father is Cantonese and Vietnamese. My son is now 3 years old and is learning Spanish in preschool. I enforce what little I know at home because his Spanish level is so simple right now.
So, basically, I speak English and very basic Spanish to him. He doesn't like it when I try to speak to him in Chinese. However, he does translate what the family says in Chinese to me (in English) :-D His dad speaks a mix of Cantonese and English to him. He was raised by his Cantonese grandparents while his father and I worked and it's actually his first language. He was so good in Chinese and so lacking in English, that we put him in preschool to catch up in English. His grandparents don't speak English. His English exploded at that point and now he's very fluent in Cantonese and English and limping along in Spanish :-)
My mother fussed and said he wouldn't learn either
language very well, but that just wasn't true. Babies have an amazing ability to pick up what surrounds them. Your son will easily be trilingual if his care givers consistently speak to him in their native languages.
One tip I read is that who speaks which language should be consistent. For example, the child might get confused if you always speak English and then one day you break out talking in Spanish. You can, for example, be the English speaking parent while his father addresses him only in Vietnamese.
This next bit is neither here nor there, but I just thought it was interesting. My boyfriend grew up speaking Cantonese and Vietnamese and learned English when he came to the US. He also learned Mandarin in Chinese school after regular school. His family speaks primarily in Cantonese and so he is fluent in Cantonese and English. However, once he wasn't living in Vietnam, he never heard the language and basically lost it. He can understand it, but he can't respond comfortably in Vietnamese. He understands bits of Mandarin, but can't speak it (and he mostly understands it because many words are similar enough to Cantonese that he can pick up the gist of what people are saying). My point is: use it or lose it. Your son needs to hear and respond in these languages for most of his life to retain the ability to use them. Even if he learns it once, and never uses it again, he'll lose it.
Anyway, you have one very lucky little boy! Enjoy every moment with him. They grow so fast!