If your project is stored in the cloud, then the simplest option would be to log in to Machine Learning for Kids when you go to school and your project will be available there.
Assuming that you're asking because your project is stored on your computer, and now you need to work on it on a different computer - I'm afraid I don't have a way to export an entire project in one go, sorry. You'll need to download the training examples for each label individually (there is a "Download" button at the bottom of each training bucket) so this gives you a file with the training data for each label. Then on the new computer, when you create a project stored on the computer, you can use the upload button at the bottom of each training bucket to restore your training data.
Kind regards