He knew she was manic depressive and had been that way for years. If she was diagnosed with "Baby Blues" for several years and put on 3 types of anti-depressives, either Russell Yates is the stupidest engineers on the planet that can't take a hint that his wife is not all there, or is too damn selfish to give a damn.
Look, people from mental institutions are barred BY LAW to work in a day-care center. Why? Because teh state doesn't want to take the chance of someone, even on medication, to be allowed to rear children, even for a few hours!
If this woman is solely to blame after having psycotic thoughts that her husband also knew about (see the knife incident) and was considered insane at the time of the murders, then how can her husband be so ignorant of the signs? He allowed his wife to do what the state in no way will allow. Thats either stupidity or selfishness. Either way its child endangerment!
Yes I agree he allowed his children to be around this deranged woman, I'm just not sure he knew until it was too late how deranged she was. I do blame him in a way for not taking her to some state hospital or at least back to her parents, somehow winning custody of those kids ---even by kidnapping them and heading for Mexico with them. No way should had have let her stay in that house with those kids around----we can all see that now, but before she hurt them, I'm not sure it was as obvious.