I have been researching some developmentally appropriate ways to teach three year olds how to hold a pencil. Here are some resources I have come across on You Tube and Teacher's Pay Teachers.
TPT Hold Your Pencil Freebie
Pinterest Pencil Grip Song Freebie
Lakeshore Learning has several great products to build fine motors skills needed for gripping a pencil. My class LOVES to feed the animals with these great products! However, you can do the same thing with materials you already have at home!! For example, tweezers and cotton balls !