It's not wrong, it's actually one of two 'best answers'. Either you had some typos or there was some bug.
To use that about a child is perfectly normal, to use it to address the child is a bit more rare, but still seems okay to me.
It could be baby, it's accepted. But 'child' fits better.
"Baby" (one that cannot speak yet) is better translated as "niemowlę" (or "niemowlak"), which exactly points to the fact that it cannot speak.