hi, I need to shoot a scene for a teen movie but my actors are tall for their ages, what techniques could i employ to make them look shorter, do I just need to raise the camera and shoot down on them slightly or is there another way?

many thanks

Go watch the documentaries for the making of Lord of the Rings, and focus on the Hobbits.

It's an interesting question, though, since you don't want them to appear so much shorter.

The real answer is to make them appear smaller than their surroundings. When casting their "parents", find 7' tall giants :p
Use large seats. Find tall countertops. Use wide doorways. Etc. Big trucks, not little cars.

Low angles tend to make people look taller. High angles make people look shorter, though it would look off if you really shot everything from a high angle.

Consider the normal placement of a camera. What? 5'? 6'? Place it a bit higher and angle as usual. Perhaps have a "regular size" person as a reference or bring a tall stick for that. //shrug.

If you can lower them in some scenes, it could help, too.

What will really ruin the illusion is the comparison to adults if they are taller, or nearly as tall.

Their actions will help too. If they seem tall and slow, like adults, won't work out too well. Have them bounce a bit as they walk, like kids. (Then again, I'm not sure what age you're going for here.)