Studies into false confessions have shown that 12 hours is the most dangerous time. Regardless of whether they've been to the bathroom or had a drink or snack, after 12 hours of questioning an innocent person is most at risk of confessing to a crime they didn't commit.
Jerry Hobbs withstood 14, but that didn't save him from 5 years in prison while a serial killer was running around killing other children. So I repeat, if you find yourself being questioned for 11 hours solid by LE, even with the odd bathroom break, the wise thing to do is end the interview and insist on going home.
And what else did LE need anyway? What questions did they neglect to ask during those 11 hours? I know full well parents need to be questioned, and I know crimes can't be cleared in an hour, but what exactly did LE expect to get in the 12th hour that they didn't get in the first 11?
It sounds to me like they had tunnel vision because the mom failed her polygraph and they were in the process of rail roading, when the husband very sensibly put a stop to it.