Unless the children of the gameobject can change during runtime, I'd recommend getting and storing the list of children in Start(), then looping through the array in your OnGUI method.
var target : Transform;
private var children : Component[];
private var toggles : boolean[];
function Start() {
children = target.GetComponentsInChildren(Transform);
toggles = new boolean[children.Length];
}
function OnGUI() {
for (var n=0; n<children.Length; ++n) {
toggleRect = Rect(0,n*20,100,20);
toggles[n] = GUI.Toggle(toggleRect , toggles[n], children[n].name);
}
}
(excuse the hard-coded rect values there - you'll probably want to modify those!)