Often, young children will complain that their writing hand hurts when working on their writing exercises. Below are a few suggestions that have helped my students.

I have young children take a break and "shake out their hands" occasionally while they're working on writing exercises. This helps their hands avoid fatigue and gives them a short break.

I also use triangle pencil grips with my students. Here is something similar that may help:  https://a.co/d/4r3swMK. I usually have my littles use these pencils: https://a.co/d/csRlmac or these: https://a.co/d/2fbsb2t.