There are many online Science education websites and many are game-based. Most have quite a bit of free content and many require that you sign up for an account, even to get free content. The ones below are some of the resources I hear the most about from teachers and parents, and there are many more listed on We Are Teachers' website.
Home Cooking and Gardening resources from Farm to School BC.
Kid's Online Learning Tools for Science, Technology and Beyond!
Kids' Engineering Games Resource Guide
The Ultimate STEM Guide for Kids: 239 Cool Sites About Science, Technology, Engineering and Math
Construction Disputes has some interesting kids activities: Construction and Building: Projects and Activities for Kids