Writing thank you notes is something that I require myself and my children to do. Not a text, not an email but a written thank you note. Before my kids could write I would ask them what they want to say and write for them. Then as their skills progressed they draw a picture or just sign there name and now my daughter can do them on her own.
I love Mummy Deals idea here of photo thank you cards. When my daughter turned one, we took pictures of her with each gift and mailed it to the giver of the gift with a note. They were adorable, plus just a postcard stamp! There are always photo deals out there and photos are much less expensive than a card.
Just a fun simple way to show your gratitude!