Some of my children are very grateful and always say thank ou, whereas others just don't seem to 'get it'. I'd say that it is a case of sloppy parenting, however it is my younger child who never fails to thank me and the oldest just seems to think that 'he has it coming to him'.

It has been awhile since I have been a parent of young children, but what I remember is that when they were younger and I was teaching them manners that they would say "Thank you" alot. It was like a game to them, and they did lip service to me. I think it is normal for older children not to say "Thank you" as much as they become abstract thinkers. Children should think that they have certain things "coming to them" such as food, clothing and shelter but they should be taught to be thankful for everything too. Sometimes they are grateful without saying anything, and they show it by being helpful. I would rather my children thank G-d for things than thank me. But I think learning gratitude towards parents fulfils the commandmentment to honor them. To get along with others it is important to be grateful to them too. So children need reminders. But listen to them when they do thank you without a reminder and be sure to give them praise, and reward them.

You can also set aside time to have discussions with them about gratitude. And teach them Psalms of Thanksgiving. Psalms 100, 117 and 118 are particularly helpful. Even a young child can memorize the first and last verses of Psalm 118.

I think that if children saw their parents thanking Hashem for the food, clothing, and other necessities of daily living, they would learn to do the same.

They do hear me make brachos and express my thanks for what I receive. They hear me thank my husband. I thank my children too, when they are helping. What makes one child more grateful than another who lives in the same household?

Some kids are naturally more "polite", or more responsive acting in the way you would like them to. Sometimes, when I do something for my kids that I don't do on a normal basis, like make a special food or dessert or take them on a trip, I'll remind them; You forgot to say something, or what do you say when Mommy does something special for you....
I always get a heartfelt thank you then!

They either express their gratitude or they don't. Usually, the same is true of other feelings.

Does your child - the one that appears ungrateful - freely express other emotions, or does he/she keep them inside? Fear? Anger? Laughter?

Especially with teenagers, they may feel uncomfortable expressing their emotions.

As much as it hurts us not to hear a "thank you", it does not always mean they are ungrateful. I am going through the same pangs. And I am very worried that this child who does not know how to express her/his gratitude will be the same with others as he/she is with us, and I hope that strong emotions, one of which of course is gratefulness, will eventually find a way out.

As Yaakov said when blessing Judah, "Adonai! It is with you that I place my hope!"

I wonder how many of us blessed with parents express gratitude to our own parents. Probably not as much as we should. If so, we shouldn't expect it from our own children.

He is very quick to display signs of discontent such as anger or his view of what is not fair. He also readily laughs.

Good point about our parents: that's an area wher i work very diligently.