hi smallsteps-
i think what you're doing is a good idea. i think what matters in actions is the motivation behind it...in your case, to protect your children.
i agree with the advice to consult a lawyer to determine if it would hold up in court. i know we have some lawyers in our midst here, perhaps one of them will let us know.
additionally, if he is drinking large amounts of alcohol at night after you and children are asleep, i would doubt that he is fit to drive to work in the morning and he would blow positive into a breathalyzer.
this surfaces an issue if he is driving the children anywhere first thing in the morning, say on saturday or sunday.
it takes one hour per unit of alcohol to wear off. i don't know his drinking patterns, but if he is downing, say 15 units of alcohol at midnight, he wouldn't be fit to pass a breathalyzer until 3 o'clock in the afternoon.
i feel it is well within your rights as a mother to express your concerns about this to the local police privately and have them pull him up one morning as he drives to work.