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Belgian Law About Babies
This is as authentic as you can get, the actual law:
You need Chapter 2, Section 3.
I'm no lawyer, but it seems to me that the child only aquires Belgian nationality if it has no other nationality. In other words, if it could acquire another nationality through it's parents, then Belgium would not grant nationality. But to be honest, you'd better check with a lawyer or someone who specializes in this sort of thing. You should probably speak to your own embassy.