My 10 month old says a few words, mama, baba, gaga. He's yet to say dada. He doesn't have a clue what he's saying he's just making sounds. I talk to him and encourage him to make all sounds.
Every single time we see mil and he says mama, mil says "dada", and keeps repeating and repeating "say dada, dada". In a tone of voice like "no, not mama, dada".