Under the law, trustees must act in accordance with the terms of the trust; act only in the best interests of the beneficiaries of the trust; invest wisely; not make any unauthorised profit; keep accounts and give the beneficiaries complete and truthful accounts.
As you are the legal Guardian of the Children and are responsible for looking after and representing the best interests of your Children until they reach adulthood, I think the law would only consider it fair and reasonable that you as the Parents were provided with the necessary information, so that the long term educational interests and welfare of the Children could be adequarely planned and managed, in order to comply with the priority and intentions of the trust fund and the main reason why it was set up in the first place, " Acting in the best interests of the Children".!
If a beneficiary has any concerns about the way the trustees are acting, the person should demand that the trustees provide an"accounting." An accounting is a statement prepared by the trustees showing how much property was originally put into the trust, how that money was invested or distributed, how much income the trust has earned and how that income has been used.
If trustees can not account for moneys they have held on trust or if they have used the money for improper purposes, then they may be legally required to repay any such money to the beneficiaries. It is possible to apply to the court for a new trustee to be appointed.
If a trustee fails to do these things, legal advice should be sought as it may be necessary to apply to the court to remedy the problem. You may need to seek legal advice in the applicable state of the US, if the trustees do not make this information available for some reason. But in the first instance contact the trustees, politely requesting them to disclose this information to you, informing them of the understandable reasons and the purposes for which you require to know these important details.