Here are some useful websites you can use
BBC Bitesize: https://www.bbc.co.uk/bitesize/primary
Science sparks has good practical activities: https://www.science-sparks.com/
http://www.treetoolsforschools.org.uk/categorymenu/?cat=activities (from The Woodland Trust)
Other suggested websites:
1- NASA Kids’ Club
NASA Kids’ Club provides a plethora of space focused games, videos, images and activities to introduce and help kids learn about the world of space.
2- BrainPOP Science
BrainPOP offers educational animated videos and lessons covering different science topics. Each featured science topic comes with illustrative videos, quizzes, and accompanying activities.
3- Discovery Kids
Another excellent source of educational video content to help kids learn about different science topics. The site also provides interactive games and links to mobile science apps for kids.
4- Science Kids
As its name indicates, Science for Kids is a website that features a treasure trove of educational science materials. These include online games, experiments, lesson plans, quizzes, science projects, free activities and many more.
5- National Geographic Kids
Nat Geo Kids enables science lovers to explore the world of science through a collection of apps, games, magazines, toys, videos, and many other materials.