If you're missing your Art lessons at school and having fun with sketch books I have linked below lots of activities to keep you busy and your creativity flowing.
The Primary Art Class (https://theprimaryartclass.com) have recorded and streamed lots of art lessons suitable for primary school age. Resources needed are items you would be able to find at home. These lessons are updated weekly, so this is definitely worth a browse through.
The Tate Kids Youtube Channel have a wealth of activities for children of all ages with professional artists giving them ideas tips on how to improve their techniques in animation, sketching, illustration. With an 'Explore, Make, Play' ethos which accessible from Nursery!
Access Art have also created a short online course for Primary school Children and adults! This is all about making a sketch book and perfecting your craft! There are also loads of ideas for children to enjoy and have a play with including a 'Continuous Line Drawing Exercise'.
The National Gallery have also added lots of resources and videos that demonstrate a vairety of skills including carving, drawing and painting the countryside.