This site provides an extensive collection of free resources, math games, and hands-on math activities aligned with the Common Core State Standards for Mathematics. Also available are Math Journal Tasks (K-5), Math Vocabulary Resources (Gds. 2-5) and Math Projects (Gds. 3-5) for teachers looking for ways to support students' math writing skills while developing key concepts and skills.
K-5 Math Teaching Resources
Grade Level Grades K-5
Great resource for a variety of activities. Be aware of the specific alignment to your grade level specific CCSS and also the rigor and relevance for students in terms of 21st Century skills.
Just be careful to view worksheets before they are printed out. Some of the worksheets have simple errors that could be caught that won't challenge or bring shame to you in front of your students.