function checkByParent(aId, aChecked) {
    var collection = document.getElementById(aId).getElementsByTagName('INPUT');
    for (var x=0; x<collection.length; x++) {
        if (collection[x].type.toUpperCase()=='CHECKBOX')
            collection[x].checked = aChecked;
    }
}

if (document.getElementById("disabilities_section")) { checkByParent('disabilities_section', true); }
if (document.getElementById("provinces_section")) { checkByParent('provinces_section', true); }