CSS for elements ONLY under a specific id

you need this:

#ParentDiv label, #ParentDiv input { display: inline; }

A comma indicates a new selector statement.

Often, so that I remember what each of the selectors is, and to make it easier to see what elements are being selected at a glance, I will alphabetize and break the selectors on two separate lines like so:

#ParentDiv input,
#ParentDiv label {
    display: inline;
}

Also, this should work just fine in IE 6/7/8, and is valid according to w3c.