My step grand daughter is just turning 2 this week.  Although she isn’t deaf, she’s been taught some sign language.  It’s really impressive seeing a 1-year-old (or younger) tell you what they want with hand gestures. 
Kinda shows that babies and toddlers are more intelligent than you think even before they can speak verbally.
For the record… I have no idea what my step grand daughter is sayin’.  I don’t know sign language.
John Vogel