You as the Settlor of the Trust can stipulate your wishes in the letter of wishes, e.g. trustee shall manage my trust fund and settle all of my medical fee during my lifetime, and after my lifetime, trustee shall distribute the trust assets to the beneficiary in a period of time with a certain percentage of the assets. If the beneficiary is a minor, it shall state clearly who is the guardian in the letter of wishes. If not being mentioned, the guardian by default will be the parents of the children.