I only have a handful of people I would call my friends. I think of them all as loving people who want to do right by me. Honestly we don't know what wappened while you were out of the room or what your friends are thinking. They could be going through a real low point over their son's diagnosis and behaviors. They had other kids there to watch over as well. Maybe the kid just freaked out. It could have all happened so fast. Mom looks away to the younger two while oldest grabs the markers. Dad sees son coloring on the desk and goes to get them. He tries but is upset and the boy has a fit. Now the parents have to wrangle three kids, deal with the mess, and are still coming to terms with their son's behaviors. They are embarrassed. In the confusion they took your words to mean not to worry about paying for the table. I'd just let it go.
I'd tell your husband you told them not to worry about it by accident. Say you don't want to take it back now.