Hi there,
"In some cases, users may see Try or Buy options on a few pages on the Adobe website. Users can ignore these options as they don't need to purchase any product or provide any payment information to use the apps.
Users can launch the installed apps directly. For example, using the Windows Start menu or the macOS Launcher." Source: https://helpx.adobe.com/enterprise/kb/covid-19-education-labs.html#FrequentlyAskedQuestions
This means they can download the apps and sign in with their school ids and they won't get any trial prompt there.
Let us know if your students are seeing trial messages even after launching the CC apps.