Explain what mama means when she talks to Walter about dreams again.

There ain't nothing as precious to me...There ain't nothing worth holding on to, money dreams nothing else-if it means-if it means it's going to destroy my boy...I'm telling you to be the head of this family from now on like you suppose to be.

Mama means that there are no dreams more important than people, particularly the well-being and emotional status of her children. Children come first.... that's the most important thing of all.