Okay kiddo, let me explain developmental differences in solitary facial expressions in a way that you can easily understand.
Have you ever heard the saying "a picture is worth a thousand words"? Well, our faces are like pictures that can show others how we're feeling without even having to say anything!
Now, when you were a baby, you probably cried a lot when you were hungry or needed a diaper change. That's because babies have very limited ways to communicate their needs, so crying is their way of expressing themselves. As you get older and learn to speak, you start using words to tell people how you feel instead of crying all the time.
But even when we're not talking, our faces can still show our emotions. When you smile, people know you're happy. When you frown, they know you're sad. Even if you try to hide your feelings, sometimes your face will give them away!
As we grow up, our facial expressions become more nuanced and complex. For example, when you're a toddler and someone gives you a toy, you'll probably smile and show your excitement. But as you get older, you might still be happy to receive a gift, but you might not show it with a big smile every time. Sometimes you might just say "thank you" or give a small smile instead.
So, to sum it up, our faces are like pictures that can show others how we're feeling. As we grow older, we learn to use more words to express ourselves, but our facial expressions are still an important way to communicate our emotions. And as we continue to mature, our facial expressions become more complex and nuanced.