Your kid is learning many things at once at this stage. However, learning appreciation is an evolving, and sometimes complicated process for kids. But the good news is that by now your kid is ready to ace in this aspect as well. For starters, he's all set to fathom that "Thank You" is more than just a word.
What you need to know
As with all developmental traits, the age at which a sense of gratitude appears will vary from child to child, and if yours is on the later side, it may just mean that your child taking longer to transition out of their egocentric stage of childhood. Personality also plays a role. There are kids who have a me orientation, the expectation that other people will do for me, serve for me, get for me, entertain for me. Despite the best of intentions, some of you foster this attitude by doing too much for their kids.
What you need to do
Most of you work at teaching your kids basic manners saying thank you and excuse me, and that’s a great place to start building a foundation of appreciation. You should keep saying thank you even for a small favor your child does for you. They will tend to learn that word and when next time you do something for your child, they will automatically say thank you, and in reply you must say - you are welcome, my dear. If Grandma and Grandpa brought something for your child, they might not be able to use words, but they could sign thank you or give them a kiss and hug.