Hi Jasminade (and others who have joined in)
If you're doing a course of 20 hours with YLs, it's a good idea to centre it around a story.
Choose one that will appeal to the age group and then plan activities, songs, games that come out of it. EG if it's raining in the story, you can teach other weather vocab, children can colour in the sun, clouds, etc. If it's about a farm, you can play "the farmer's in his den", teach vocab of the animals on the farm. If somebody goes shopping in the story, you can do a little role play in the shop, and look at what is sold in a toy shop, a greengrocer's etc. I'm sure you get the idea.
If the course is longer than 20 hours, you'll probably need a course book.
If your school is doing YL's for the first time, you'll need new materials, eg plastic fruit, kitchen equipment (or whatever for teaching vocab), you'll need scissors, card, glue etc for making things with the YLs ( unless you ask the children to bring them)
good luck, I'm sure you'll have fun