How do I find a Part inside of a few Models?

How would I make a script to go into Models (with different names) and find a Part named "Head" inside them? And then turn them Transparency = 0?

local ting = 0  
owner = script.Parent.Parent.Parent.OwnerName

function onTouched(hit)

    if ting == 0 then -- debounce
        ting = 1 -- debounce
        local check = hit.Parent:FindFirstChild("Humanoid")

        if check ~= nil then -- debounce
            local user = game.Players:GetPlayerFromCharacter(hit.Parent)
            local cost1 = script.Parent.Cost
            local cost = user:FindFirstChild("leaderstats"):FindFirstChild("Dollars")
            local user = game.Players:GetPlayerFromCharacter(hit.Parent)

            if (user:FindFirstChild("House") ~= nil) then 
            local user = game.Players:GetPlayerFromCharacter(hit.Parent)
            user.PlayerGui:FindFirstChild("AlreadyOwn").Frame.Visible = true

            elseif user:FindFirstChild("leaderstats").Dollars.Value >= cost1.Value then
                owner.Value = hit.Parent.Name
                cost.Value = cost.Value - cost1.Value   

-- the below should find "Head" inside of models of script.Parent.Parent.Parent and make them seen
                    for i, v in pairs(script.Parent.Parent.Parent:GetChildren()) do
                    if v:IsA("Model") then
                    for ii, vv in pairs(v:GetChildren()) do
                    if vv.Name == "Head" then
                    vv.Transparency = 0
-- finding "Head" ends here

                local own = Instance.new("NumberValue")
                own.Name = "House"
                own.Parent = user
                own.Value = script.Parent.Sell.Value
                local ownshouse = Instance.new("NumberValue")
                ownshouse.Name = "OwnsHouse"
                ownshouse.Parent = user
                ownshouse.Value = script.Parent.Parent.Parent:FindFirstChild("Value").Value
                user.PlayerGui:FindFirstChild("HousePurchase").Frame.Visible = true
                script.Parent.Parent.Ad:remove()
                script.Parent.Parent:remove()
                local home = game.ServerStorage.Home2
                home.Parent = game.Workspace

            elseif user:FindFirstChild("leaderstats").Dollars.Value < cost1.Value then
                user.PlayerGui.NotEnough.Frame.Visible = true

            end
        end 


    ting = 0 -- debounce


    end             end
                    end
                    end
                    end


end

script.Parent.Touched:connect(onTouched)





This code errors:
Script:33: attempt to index field 'Parent' (a nil value) -- no idea why.