So I went to Amazon and bought pencil grips that I've used with students in the past. They work very well and position the child's fingers correctly by using finger holes. My son has done really well with these grips and is starting to hold the pencil correctly even when he doesn't have the grips on. Just remember, the big hole is where the thumb goes.
I'm also a fan of the large beginner pencils which are easier for little ones to grasp.
It's important to teach your child the correct way to hold a writing instrument from the beginning so they don't have to relearn when they get to school.