This link will take you to a free app. Khan Academy Kids is a newer app (an extension of the well known learning website, Khan Academy) designed for young students. It is a great way to get some educational technology time in for your kiddos!
Parent Challenge: Create some bonding time with your child by cuddling up for fun learning together!
Starfall is a fun educational website to explore. It does have limited content without a membership, but my own kids still love what is available within the limited content!
This website offers fun educational games and videos/video clips.
Heads up: This site is only free on a PC, not a tablet or phone. If you install the app on your tablet or phone, they require a membership.