"In your trust" as s beneficiary, right?
Kids can't be trustees.
Only Trustees can possess and transport the NFA items.
Yes only Trustees can possess and transport NFA items but minors can be listed as Trustees. Minors must wait until they are of legal age to possess NFA items. This does not prevent you from listing minors as trustees and beneficiaries. I had this talk with Dean last week when he was creating my trust.
I am not sure if this is specific to how Dean writes his trusts, the same way that his trust states that only the Settlor can purchase NFA items and not the co-trustees. Co-trustees can only possess.