The phrase "one's little mouth" refers to someone's ability to speak or voice their thoughts and opinions. It suggests that the person has a small or limited voice or influence in expressing themselves. Full definition
This 100 % silicone pacifier is soft and flexible, making it perfect for little mouths that haven't developed any teeth yet. (abckidsinc.com)
The shallow spoon bowl is just small enough to fit in little mouths, yet deep enough to scoop plenty of food for a frustration free meal. (tinyfry.com)
These were wonderful to get into the tight spaces of little mouths without breaking and taste great. (businessinsider.com)