First, where are you posting from? Where ever it is from delete the MN history (but not anything else) and dont save your password. If you are using a PC then go to the start menu, click "all programs" then the folder marked "accessories", then "ease of access". In there is an on screen keyboard that you can use with the mouse that wont register if he has put a keylogger on the pc so he cant read anything you type. You might think he wouldnt do that, but he would, he really would.
Secondly, what are the arrangements in your house re the kids and work? Do you work or are you main carer for the kids? Does he work? If you are the main carer then it would take an awful lot (sustained and proven abuse or neglect) for him to get custody of them. If he is the main carer then that is more problematic but not insurmountable. do you have an access to any money, preferably in cash?
Thirdly, escaping. If you rocked up tomorrow with the kids and a bag, would they take you in and put you up? In preparation get together all the paperwork you can feasibly get without arousing his suspicions, so birth certificates, passports (very important if you think he may abduct them), mortgage info, rental agreement, credit card and bank statements...anything you can get. As for the kids, yes it is a big change, but nowhere near as traumatic as growing up with an abusive father and a bullied and abused mother. You need to do this for them, they are suffering more by you staying than if you leave.
Lastly, call Womens Aid when it is safe for you to do so. DO NOT WRITE THE NUMBER DOWN, another MNer in your position did this and he found it....you can imagine the rest :( bear in mind that if you call from your mobile it will be charged and will show on your bill.
Keep posting sweetie, we will help you get out of this.