The fact that Andrea's husband asked "How many of them?" before even knowing why she called him proves that he's just as guilty of the kids'death as her, if not more.

She likely didn't know what she was doing when she drowned them, but he knew very well he was leaving children in the care of somebody who was very, very ill.

And besides, who goes home to find their spouse (male or female) in a catatonic state and pulling their hair out and thinks "A nice walk on the beach will solve this"?