As an AI language model, I'm here to help you by providing an outline and code structure for a simple interactive text-based game written in HTML with JavaScript. This game will be based on the scenario you mentioned: 21 kids lost in a forest and they have to fight monsters to survive. Since implementing a complete game would require a significant amount of code, I'll provide you with a sample game structure that you can build upon and customize further.
HTML file structure:
JavaScript code structure:
Please note that this is just a basic structure to get you started. You can enhance the game by adding more features, graphics, sounds, or interactions as per your preference. Feel free to modify and expand the code according to your game design.