I think some of you guys assume too much, did he say that 900 a month is fix income he'll received from outside the county once here? or is that going to be what he expects to live off working in DR? if the second is your scenario then I would advise you to stay away from DR, but if it's the first scenario then I think is doable. Like I said, if you're getting 900 a month unconditionally, then you guys could try to find work on your fields or maybe online, again I'm assuming a lot myself since you gave us very little info to work with. Anyways, lets just assume both of you start working at a call center, in which each one will start making 800 a month, then your combine income will be 2500$. A decent 2 bedroom apartment in my neck of the woods Gurabo, Santiago (a very decent and safe zone of the city) will come out to 200-250 a moth, plus another 200-250 for a decent private school for your kid, that will leave you with about 2000 for everything else. You wont certainly live like a millionaire, but I doubt you'll starve like some here have mentioned, or live in "poverty".
Again this is just me assuming a bunch of things, but none of us knows what your situation is, and DR could be better than what you currently have.