From a sermon from 11/9/14
It is unwise to judge how thankful our children are by how pleased they are. Children are not spiritual in their thinking and they are pleased most at what their flesh wants, not what God wants. When you have given your children a gift, their true thankfulness cannot be measured by how happy they are that they got a gift. Their thankfulness can be measured only by how glad they make you that you gave it to them.
Our thankfulness toward God is judged this way. Think about it. The last time God gave you a blessing, how glad did you make God that He blessed you?