Holding a pen
This is the grip that you can encourage your child to have (please do not correct them every time).
You can encourage them to make a puppet/crocodile with their hand.
Then the puppet/crocodile grabs the pen to eat!!
If your child is working on paper, angle the paper to help them.
Below is an example for left handed children, but it benefits right handed children too (remember to angle it in the opposite way).