Welcome to YorkieTalk!
Some Yorkies are just quieter than others. Henri is a little over 2 years old and is pretty quiet, he rarely barks. My Grandma came for a visit and kept commenting on how quiet he is, she kept saying to Henri how he is such a good boy for being quiet

He really only barks or growls when he is "protecting" the house or me.
If your baby is one of the quiet ones then count yourself lucky, there are other dogs in my family that are the complete opposite