One way to teach gratitude to younger kids is by having them make handmade cards or gifts for their teachers. I did this with my daughter when she was younger. She is ten years old now and she makes handmade cards/gifts/baked goods for her teachers on her own every year during the holidays. I hope that my boys will also follow her lead some day.
With my four year olds, I try to keep the activities fun and interesting so that they participate willingly in them. This year, we used felt, pom poms, googly eyes, card stock, glitter glue and scissors for the materials. I gave them old toothbrushes (both electric and non-electric), paint brushes of various sizes and squeezable glitter glue bottles to paint. I could tell that they really enjoyed this activity. And they were proud to share their hand made cards with their teachers. We also made Christmas tree ornaments (not in the picture) using small golden jingle bells, beads and string. Another simple and fun activity for four year olds.