I also teach 8 year old twice a week, I have apair of girls that are very restless and are constantly twitching and moving.
I also know that using flash cards can only help for mayb the first 10 minutes of your class to introduce laguange used.
The best classes I have had are actually using board games.
Go find a store that sell English versions of Monopoly or any board game, they must use their English to communicate and they have fun doing it.
Games like 'Sorry' work well. 4 colors each colour has a meaning. If you land on a red square they must tell you the name of a fruit.
My students love Jenga, Write a topic on the board and they must make sentence with that topic.
time expressions go through alesson teaching, IN/ AT/ ON/ SINCE/ Ago.. and so on.
Then they must make sentence with those words. When they use a noun wirite it down so they cannot use the same noun more than once.
If they say, Yesterday I went to school at 8:00am.
The next person cant use, 'yesterday' or 'school'.
If their sentence is wrong they remove a block from the jenga tower, if it is right you take one. They love to try and defeat the teacher.
I hope some of these ideas help you as I know that age group can be very rediculous to teach and getting them to stay still is a challenge in itself.