If the trust was set up as an irrevocable trust, the entire trust assets would be out of the deceased's estate, unless the trust is deemed to fail later in the court. Then all child support issues would be out of question, unless it is speficially provided for in the trust provisions. Of course, if the court wants to come in and invade the trust assets, that's always possible. However, it really depends on the purpose of the trust, when it was set up, how it was set up, who are the grantor, trustee, and beneficiary, among other things. I just don't believe it can be codified in any US states regardless the circumstances.
I think you are confused with the concept whether the trust is part of the deceased estate. It can be part of the estate for estate tax purpose, but it may not be part of the estate for other purposes. Also the fact that the grantor paid income tax for the trust tells me nothing with respect whether the trust is revocable or irrevocable. There are certain drafting techniques to make the grantor pay the income tax for an irrevocable trust, while at the same time removing the trust assets from the grantor's estate.
I believe you know much more than was posted here. Probably that's why you came to this conclusion. All I want to point out is that without seeing the actual trust document and understanding the background of this trust, it would be very difficult to provide any meaningful legal advice, let alone it is to a layperson.
