You've got both my hands OP!
Does he work? If he's going to work tonight/tomorrow that might be a better option? (he's out of the house for several hours)
You need to leave with a clear plan (speak to bank about any joint accounts, find yours and children's passports and any other important docs, prescriptions, etc)
If I were you, if your parents are supportive, phone them or a close friend. Tell them to meet you at the house and then you can leave with them, or at the very least they can keep the children out of the way (in car) whilst you tell husband you're leaving and then you safely get into car.
If you're in a rented house, I would just leave. But you do need to get your name off that lease in case your husband does something stupid and you are held responsible. (Tell landlord/agent you moved out on X day (today/tomorrow)
I wouldn't pack and 'prepare' leaving whilst your husband is there, he will try to stop you and things could get ugly/violent. Is it possible to wait until he leaves the house? Maybe his mother could call him over to 'help' with something or you could give him an errand to run that could give you a bit of time to prepare yourself and get family over to help you?