The activities listed would be helpful, but not required to continue your child's academic growth in third grade.
Math:
Moby https://www.mobymax.com/signin School Code: va600 The Username and password are your child’s student number.
STEM and Math resources http://bedford.sharpschool.net/departments/inst/s_t_e_m
Sumdog https://pages.sumdog.com/
Prodigy https://www.prodigygame.com/
Reading and other fun sites:
Scholastic Learn at Home https://classroommagazines.scholastic.com/support/learnathome.html
Virtual Field Trips https://docs.google.com/document/d/e/2PACX-1vTbUBsKt4U5tR-eXC8b2bogrvjrVlEBl8OJIesNPw6b7BRScYRuyXIaSAVIcl_q52BI4SqrK4_HVQCw/pub?urp=gmail_link
Typing Club https://www.typingclub.com/
Fun Poetry Activities: https://www.poetry4kids.com/#
A variety of online resources, mostly with authors and illustrators: https://docs.google.com/document/d/1OH-_GM-eYefOa7JDNmM6wdUb9fsa1H8k8O_XgPih4m0/mobilebasic?urp=gmail_link
SCREEN FREE IDEAS:
Write to a friend or family member who could use some cheering up.
Measure things around your house and keep a log to find things that are less than a foot long, a foot long, and more than a foot long. You could change the measurement to 1 inch, 1 cm, 1 yard, etc.
Read a book to your sibling or a pet.