Here is a suitable English birthday invitation for 5th grade students that is not too long or too short:
Birthday Party Invitation
Dear friend,
You are invited to my birthday party!
When: Saturday, June 10th
Time: 3:00 PM
Where: My house, 123 Elm Street
We will have games, cake, and fun!
Please come and celebrate with me.
Hope to see you there!
From,
[Your Name]