Don't I have the right to know about my children's trust fund?

The short answer is no, but you may be able to demand that the trustee provide an accounting if you feel there has been mismanagement or self-dealing. That demand would probably be made in a probate court, not a family court.

I don't think there's a cut-and-dry answer to your question, especially without more information. As the mother of his children, it's saddening that he is being secretive with regard to the trust. If the children are minors, as their legal guardian, you may be able to demand an accounting of the trust on your children's behalf. However, some trusts are written in such a way that the trustee does not have to provide an accounting at the beneficiaries' request. It just depends on the wording of the trust. I think you'll have a particularly difficult time if the trust is a Revocable Trust. If you think action needs to be taken to protect the rights of the children under the trust, then you should contact an attorney in your area to see if you can get some movement.