Middle school students are old enough to help with project planning and execution. Use this to your advantage. Involve students in your PTO/PTA events and activities, let them take some ownership and help the event be successful.
The middle school’s student council president would make a great student representative to your PTO/PTA executive board. Also have a PTO/PTA member attend student council meetings. When everyone is on on the same page you can work together for the betterment of the school.
Remember maturity comes with age. There will be different maturity levels between the 6th and 8th graders.