Chess sets
There are numerous outlets from which to buy chess sets. The larger pieces are better for teaching children. It is the opposite of what you would perhaps expect. I would recommend the standard tournament-size chess pieces with roll up boards. You can find school multipack sets which provide 10 chess sets.
An example of this can be found here:
Mega Club Combo A (10 chess sets, roll-mats and bags) / Chess & Bridge
Demonstration boards
If you are going to be a teacher, you should ideally have a large demonstration board for your lessons. Your school club class time should be divided between demonstration board lesson and playing. More details on structuring your class can be found elsewhere.
Suitable demonstration boards can be found here:
Chess Demonstration Boards / Chess & Bridge
There are various online teaching demonstration boards available on Lichess and chess.com. Some schools will allow you to use these on whiteboards in the school.
Scoresheets
Firstly, if you are using an online and real demonstration board, your children should be getting used to answering question using coordinates. This will help the children write their moves down for their games. Using a scoresheet to have a copy of their game is not something you would use for beginners. However, it is essential for players who are competing in school teams and individual tournaments outside of school.
A possible example can be found here:
Duplicate Chess Scoresheets x 100 (No Carbon Required) / Chess & Bridge
Some children prefer their own scorebook. A suitable choice would be:
100 Game Chess Scorebook – Hardback / Chess & Bridge
Clocks
The children really like using clocks in school chess club, but they are not essential for a standard school club. However, if some of your children are playing for the school team or in external tournaments, then tournament practice using clocks is essential. For school chess club, any cheap clock would suffice. You can normally get discount deals for bulk buying from most providers.
An example would be:
DGT Easy Plus Digital Chess Clock / Chess & Bridge
Rewards
Children love rewards in school chess club; anything from stickers, house points or golden time if the school allows you to reward them as part of school procedure. You can also bulk buy lots of very well priced small toys, such as bouncy balls or stretchy men.
NOTE: Under no circumstances should you be giving out sweets on a school chess club.