How to check for a number of objects?

I am making a game management system kind of like RDS and I need help figuring out how to find the number of children in an object. Here is my script so far:

local playerNum = game.Players.NumPlayers

while true do
    wait(1)
    for _,p in pairs(game.Players:GetPlayers()) do
        if not script.Parent:FindFirstChild(p.Name) or p.Name == game.Players.LocalPlayer.Name then
            local button = Instance.new('TextButton')
            button.Parent = script.Parent
            button.Name = p.Name
            button.Position = -- This is where I need to figure out the number of objects before continuing
        end
    end
end

In StarterGui, this is what my explorer window and view looks like:

Explorer window: http://i.imgur.com/352MOhc.png

Player view: http://i.imgur.com/t2aUisg.png