In an effort to help parents stave off the dreaded "summer learning loss," a variety of free programs are available online, and more are popping up all the time. Here's a list of some of the ones I've come across to help keep your kids learning and occupied throughout the summer:
Start with a Book: This site has printable Reading Adventure Packs for grades K - 3, covering a variety of topics, including Bugs, Birds, and Animals; Flight; Time and Time Travel; and others (24 altogether). You'll also find links to hands-on activities, writing prompts, websites and mobile apps.
CK-12 BrainFlex: Sign up to practice math and science skills.
Summer Playlists: Power My Learning has collections of online activities for all the main subjects.
Electric Company: Their summer learning program includes YouTube videos and corresponding worksheets for math and vocabulary. A guide and other PDF resources can be downloaded from the main summer learning page.
Camp GoNoodle: Each week in July, you receive an email with new adventures and activities, both online and off, and the ability to earn badges.
Self-Learning for Kids: Not really a program, but a very long list of free, self-learning online resources for kids in pre-K through sixth grades. There are 75 resources, organized by type.
(More resources listed in comments sections below)