In his book, A Woman's Wisdom, Rabbi Arush writes about the value of training thankfulness in a child. Here are some quotes:
"You should teach your child to say a proper thank you to God, to mommy, and to daddy for something as simple as a cup of water. That way, the child learns not to take anything for granted and grows up appreciative, unspoiled, and happy with whatever he has. Such children are never jealous or disgruntled.
“By contrast, parents who don't require this are almost guaranteeing that their child will acquire terrible character traits—lack of appreciation, an inflated sense of entitlement, jealousy, anger, and ingratitude. The child that never learns to appreciate and say thank-you becomes a spoiled child who is always yelling and demanding to have things that don't belong to him. Today, he's maladjusted in kindergarten and tomorrow, he's a self centered, hateful individual that's on the way to his second or third divorce.
“Parents themselves can become so sick of their own spoiled child's ingratitude that eventually they stop wanting to give anything to their child.
“The child needs to say the thank you more than any adult will ever need to hear it, for the child's own sake. To be required to SAY it, by wise parents, is good for the soul of the child. Just as praise is becoming to the righteous—their face beams while doing it—so is thankfulness on the lips of a child.”