On this site, you can search over 3,500 of the very best science and math activities on the web. Find handpicked activities from your favorite science museums, public television stations, universities, and other educational organizations. All activities are available free of charge. Source: https://www.howtosmile.org/
This curated collection of free learning resources from NHPBS and PBS includes standards-aligned videos, interactive content, lesson plans, and more, for all grade levels. Source: https://nhpbs.pbslearningmedia.org/
Here are a couple of links to help parents get familiar with Google Classroom and finding learning material online.