Surely all biological parents' kids could be identified from the parent's DNA? Or failing that, grabbing basically anything from the kids house/room: tooth br

Surely all biological parents' kids could be identified from the parent's DNA? Or failing that, grabbing basically anything from the kids house/room: tooth brush? hairbrush? shoes/socks? these all seem like easy ways to get a DNA sample from a parent for their child. I guess the fingerprint part might be useful?