According to Nutureshock, the thing where babies tend to say nouns first has more to do with the English language than this being a general rule (because in English setences tend to end in verbs).
DD's first word was "up" and she's said quite a few verbs in both DH's native language and English. I think what your child is interested in also plays a huge roll AND how easy it is to say certain things, e.g., she picks the easiest words in our respective languages to say. I think mama and dada tend to come first just because they are easier to say.
