You can get a parenting order that stipulates who is and isn't allowed parental responsibility for the short term until a court case is decided.
Also contact your childrens school, explain the whole situation and ask them to contact you the moment he sets foot in the school.
If all your kids go to the same school they may have procedures in place to ban him from the premises, so ask about that. Also contact your liason officer from the police and ask what other help and protection you are entitled to.
Speak to Victim Support as well.
Basically, if you ask everyone you can think of, somebody will know a way to stop him being able to take them.
If all else fails is there anywhere away from where you live that you can take the kids until after the trial?