Problem Addressing Objects Using ChildNodes

i'm working on a portion of a CMS that allows content-admins to browse
a product list, and add individual products into the taxonomy by
clicking checkboxes next to categories they might belong in.

since the taxonomy is a rather long list, i'm hiding and showing divs
for the secondary and tertiary links, so when a user clicks on the
checkbox for the parent category, the children appear in a second (and
third) div, with checkboxes of their own.

however, i'd like for the secondary and third level checkboxes to
become unchecked when the parent is. i've tried addressing them in
numerous ways, but something consistently gets lost, in that i keep
getting "x doesn't have any properties" errors.


ie:
var parentnode = document.getElementById(divName);
var allMyChildren = parentnode.childNodes.getElementsByName("INPUT");
alert(allMyChildren.length);

this returns the proper length, but then

for (var i=0;i < allMyChildren.length;i++) {
var chklist = allMyChildren[i];
if (chklist.type == "checkbox") {
// uncheck it
}
}

this consistently returns that chklist has no properties...