There are a variety of open educational resource (OERs) available online. OERs differ from other “free” resources in that they are intended to remain free and open in the public domain, unlike the bait-and-switch we’re all used to with other “free” tools. These resources can range from open textbooks to online simulations and assessments. Many are of sufficient quality to replace other paid resources.
One such collection of resources for K-5 learning exists through REMC, and you can find a grade- and subject- oriented list on MiTech Kids (https://www.remc.org/mitechkids/). These resources were collected with the Michigan Integrated Technology Competencies for Students (MITECS) in mind and can be a first step to building technological competencies in your students that will propel them to greater heights throughout their life of learning.