I think seven-year-olds should start to feel gratitude, they are bad enough at eight, without them not realising what Adults contribute.
I specifically don't want my son to feel gratitude to me on Christmas morning. He's thoughtful and grateful enough all the time. He sees what I do for him and knows he can't do as much for me which makes him feel sad and inadequate sometimes. He is desperately sad on my birthday that he can't give me a gift that measures up to what I give him for his. I want his Christmas morning to be free of that stress. Santa does that. I want to give to him and give 100% of the credit to a myth. But you know, if you give with joy, children learn to give with joy. It never occurred to my parents to give to us on Christmas with the expectation of gratitude. They just gave with joy and as an adult I'm in awe at that pure expression of love and want nothing more than to make that same expression to my son.
Someone coming along all po-faced and telling my son what he should and shouldn't be feeling is a massive over-step of their role in his life. In fact, if I tried to do that it would be an over-step of my role. His feelings are his own. And gratitude that someone has been lectured/shamed into being supposed to feel isn't genuine. And compelled gratitude is worthless compared to gratitude that has been genuinely realised.
I would feel as though I had let my child down, in terms of understanding how the World works and what shit lives/poverty a lot of people have, at that age. Critical thinking should be encouraged from a young age.
Hahahaha! I'd think I'd let my kid down if he grew up to have this little understanding of cause and effect, empathy and just the very basics of reality. Fwiw, I believed in Santa until I was 11.5 and grew up to be a super sceptical atheist, involved in investigative journalism in my early 20s and broke a very important news story involving war crimes related to the middle east. In my mid-20s I moved into international development, then domestic poverty alleviation through my late 20s. I now work in education research, working on ways to ensure that children can meet the standards set by the curriculum without negatively impacting on how they play and use their imagination. Because a the growing body of evidence shows just how very detrimental it is to have that part of your childhood ended too early.* I'm also not a complete arsehole who tries to make others feel like shit for their most innocent parenting choices. 
*I'm not implying there is anything wrong with not believing in Santa. It's not any sort of essential myth and it's fine to stop believing early/never believe and doesn't mean a child doesn't have a healthy imagination of their own. But equally, there is nothing wrong with a child continuing that suspension of disbelief right through to the preteens if they choose to.