There are many educational sites online, some are free to educators and some are not. Here are few that might benefit you. Also, doing a Google search for 1st grade educational resources and the like will bestow many more.
General
Google for Educator Help Forum (if you have issues, more than likely, others have problems too - check out the forum for fast answers)
Twinkl (free resources and more)
EdPuzzle (a plethora or resources, free and paid)
Reading and Literacy:
Allkidsnetwork.com (Great website to print out worksheets)
Math
Hundred's Chart (Practice counting by 1's, 10's, and 5's - PDF)
Imagine Math (provides 100's of DL-based math lessons at your fingertips)
History
Best Educational Social Studies Websites (ideas and projects galore)
Science
California Academy of Sciences -Highlights for K-1st Grade (science lessons and more)
The Best Science Website for Elementary Students (videos, experiments, and more)
ADDITIONAL RESOURCES:
Art for Kids Hub - (Watch step by step directions to create beautiful art)
Teacher Vision (this looks like the backdoor to the service, but you will at least get an idea of what the company offers)