Yes. Your will affects any assets that are titled in your name at your death and are not in your living trust or some other form of ownership with a right of survivorship. If you have a living trust, your will would typically contain a pour over provision. Such a provision simply states that all such assets should be transferred to the trustee of your living trust after your death. (This does not mean, however, that your beneficiaries can avoid going through probate for these assets.)
Your will can nominate guardians for your minor children as well. Any assets held in a trust for your children would still be managed by the trustee.
To find out more about wills, see the State Bar’s consumer pamphlet entitled Do I Need a Will? For information on ordering a copy of this or another State Bar consumer education pamphlet, see #1 above.