If you are using latex caps, switch to silicone ones. If you are already using silicone caps, try a Lycra or polyester cap since it sounds like they are both overly sensitive.

One kid complains that the swim cap I get for teen is too small/tight for his big head, and he wants me to buy adult size. It hurts everytime he puts on his head. He is age 8.

One kid complains that it causes her head really itchy when it is put on, and she has long hair. She is age 5.

I need swim cap recommendation for both kids, thank you.