How soon can my child get a cavity? Written by Website Administrator on July 12, 2012. Posted in FAQs As soon as the tooth erupts from the gum, plaque can begin to build up if oral hygiene is not properly maintained. Trackback from your site. Website Administrator This information box about the author only appears if the author has biographical information. Otherwise there is not author box shown. Follow YOOtheme on Twitter or read the blog.