Army and USMC platoons will all have one officer (PL, platoon leader, LT..etc) And at a platoon sargent in charge off all the other NCOs traning, lagistices and platoon attachment.
A US army light infantry, Airborne and Stryker platoon will have 4 squads. Each lead by a squads leader (NCO)
And then 3 of the squads will be line squads comprised of two sections or fire teams. Each will have a team leader (usual an NCO or soon to be promoted E-4) a riflemen, SAW gunner and a grenader.
The 4 squad is the weapons squad, lead by at least one NCO. This squad may or may not have another 5 on a gun team. Ideally not. All the other NCOs would be attachment. FOO, may or may not be an NCO same with the medic.
An armoured infantry platoons order of battle escapes me at the moment.
I can not vouch off the top of my head how many NCOs are in a USMC platoon but they do have 3 sections per a squad makeing there squads 13 men strong where as the armies 9 men strong. At least 4 of the men would be NCOs in a perfect world.