Parents who attend their children’s competitive sports events are the best of fans, yet it could be argued that this puts more pressure on the children. As the captain of a sports team, you have speak at the Parent's Association about this situation

Define the format and audience: Speech/Parent's Association

Precise the issue: Kids have more pressure when parents go to watch their competition

Then you can start writting down ideas. I suggest starting by welcoming the audience. Then you present the problem. Remember that this is a speech and it should touch our hearts while it conveys the message. Make it personal, maybe use anecdotes that will connect you to the audience. Once the audience is familiarize with the problem you can start proposing solutions, and maybe give your own opinion. Finally, close the speech by emphasising how by solving this problem we will help our kids. 

Remember that you are restricted by around 400 words so you have to be straight forward