Best protection is to keep everything separate.
...and the best way of doing that is not to get married, oh! too late.
I must be living in a parallel universe - since when did it become acceptable for someone to get married, giving their spouse and children the (quite reasonable) expectation that they will live as a conventional married couple, only to decide after the wedding that they don't fancy compromising after all quite yet, (but maybe, one day, they might, we'll have to see) and in the meantime, protect their own assets at all costs?
OP you made a mistake by marrying your DH. Your DCs and your DH will suffer the emotional and financial consequences of that, even if you manage to avoid them. I could understand it if it were a spontaneous, shotgun wedding (Brittany Spears style) but you sought legal advice and put a prenup in place; hardly a spur-of-the-moment decision, was it? Less a romantic whim, and more of a business transaction, really?
It's no surprise the DCs are displaying emotional anxieties - they must be totally bewildered; their parent has got married, but carry on as if nothing has changed? Their whole belief system about marriage and relationships has been challenged, and no one is explaining anything or supporting them to make sense of their confusion. Avoiding addressing the issue in case it upsets an adult is a catastrophic failure as a parent - these children need explainations and assurance - at the moment they have uncertainty and ignorance.
No matter what the opinions or advice given on this thread, the fact remains that you need legal intervention to extract yourself from the situation you have created. You may face a judge who is sympathetic to your cause, or you may face a judge who feels, like I do, that you have treated your DH, and your DCs disgracefully, and should face the consequences. Judges are human too, and their opinions do influence their judgements.