Can I as the beneficiary of my children's trust fund's borrow from it to stop forclousure

The answer to that is going to depend on the terms of the trust, and the discretion of the trustee.  If this trust, for example, was set up to provide for your children, and you are also a beneficiary, then you might be able to borrow from it to prevent a foreclosure of the house in which your children live.  You should review the trust and speak with the trustee.