DD's first word (and still her only reliable one, although she has a go at others) was "yes", which she has been saying since about 10 months. it makes her a very amiable conversationalist.
my DN's first word was "shoes" and she's still obsessed with them now.
my DB's first word was "hot" (we lived in Yorkshire at the time, so he pronounced neither the 'h' nor the 't') and he thought everything was 'o'. It took us ages to understand why he thought the sky was hot, until we realised he thought the clouds were steam.
What about your lot??