In the end, the money, converted to negotiable bonds, was destroyed and the step-children left their mother, dejected. The doctor of the establishment decided that Ethel wasn't insane, just essentric, and so will release her. And it turns out that the nurse stole the bonds, faked their destruction, and gave them to Ethel so that she could use them as she sees fit. The pseudo-happy ending all around. Except it shouldn't be.
But perhaps the children deserve what is done to them. But nothing is shown to show us how bad the children are. Indeed, Ethel takes delight in tormenting them about the missing money. Ethel is the villain in this play. Indeed, she sends one of the children into a chimney claiming the money is there. Later we learn that the chimney collapsed onto the person. I thought he had died and Ethel was happy at the result, but we later see him alive with a broken arm. She still doesn't feel bad. Is that the actions of a sane person? I think not.