A month or so ago I made a fun emoji pillow project with the hopes of it helping my littlest guy express his feeling. Well, it worked.
At first it was a toy; he'd have fun playing with it and giggle when we switch from happy to sad faces. Then he started using it to tell us how he was really feeling. After a temper tantrum, usually through tears, he'd eek out, "Me happy now," with his arms outstretched looking for a hug.
It is his way of switching gears and starting over. There's nothing wrong (in fact it's an essential part of living) with feeling bad when you've acted poorly or made mistakes, but it is not healthy to hold onto those sour emotions after their importance has dissipated. I tell my kids all the time, "be like Elsa and let it go."
Back to the little one, since he's mastered the basic emotions we thought we'd introduce him to a few more by creating a Feelings Wheel, or Circle if you're looking at the pictures. It's super easy to make and perfect for older kids to put together.