What's wrong in this heat vision goggles script?

Here's scrpt:

local guiMain = Instance.new("GuiMain")
guiMain.Name = "ThermalGuiMain"
local mode = 0
local thermal = false


function lastParent(obj)
	local object = obj
	local parent = object.Parent
	while true do
		if parent == workspace or parent == game.Lighting or parent == nil then
			return object
		else
			object = parent
			parent = object.Parent
		end
	end
end


function selectAllPartsOfHuman(obj)
	if obj.className == "Part" or obj.className == "Seat" or obj.className == "TrussPart" then
		local selection = Instance.new("SelectionBox")
		selection.Adornee = obj
		selection.Color = BrickColor.new("Really blue")
		selection.Name = "Selection "..obj.Name
		selection.Parent = guiMain
		if obj.Parent:findFirstChild("Humanoid") ~= nil then
			selection.Color = BrickColor.new("Really red")
		end
		obj.AncestryChanged:connect(
		function()
			if obj.Parent == nil or lastParent(obj).Parent ~= workspace then
				selection:remove()
			end
		end)
	else
		for i,child in pairs(obj:getChildren()) do
			selectAllPartsOfHuman(child)
		end
	end
end

function onKeyDown(key)
	if key == "t" then
		if mode == 0 then
			if thermal == false then
				thermal = true
				selectAllPartsOfHuman(game.Workspace)
			elseif thermal == true then
				local child = guiMain:getChildren()
				for i = 1,#child do
					child[i].Visible = true
				end
			end
			mode = 1
		elseif mode == 1 then
			local child = guiMain:getChildren()
			for i = 1,#child do
				child[i].Visible = false
			end
			mode = 0
		end
	end
end

function onEquipped(mouse)
	local player = game.Players.LocalPlayer
	if player.PlayerGui:findFirstChild("ThermalGuiMain") == nil then
		guiMain.Parent = player.PlayerGui
	elseif player.PlayerGui:findFirstChild("ThermalGuiMain") ~= nil then
		local child = guiMain:getChildren()
		for i = 1,#child do
			child[i].Visible = true
		end
	end
	mouse.KeyDown:connect(onKeyDown)
end

function unEquipped(mouse)
	local child = guiMain:getChildren()
	for i = 1,#child do
		child[i].Visible = false
	end
end

function updateChildren(new)
if mode == 1 then
selectAllPartsOfHuman(new)
end
end



game.Workspace.ChildAdded:connect(updateChildren)


script.Parent.Equipped:connect(onEquipped)
script.Parent.Unequipped:connect(unEquipped)

I don't know if the script is still working, because I was programming it a long time ago.