How can I GetChildren of a Folder everytime a new Child is put in?

I am trying to do GetChildren() on a folder, but it comes back as nothing. The folder constantly has Sounds going in and out, so how would I go about trying to make it find the Child every time a new Sound is added into the folder? I already tried combining the scripts, but it was a mess.

Here is the script that works with the Folder, it puts the cloned Sound into the Current Song Folder:

local starterGui = game:GetService("StarterGui")
local shuffleBtn = script.Parent

local musicFolder = starterGui.MusicGui:WaitForChild("MusicFolder")
local songs = musicFolder:GetChildren()

local currentSongFolder = starterGui.MusicGui:WaitForChild("CurrentSongFolder")

shuffleBtn.MouseButton1Click:Connect(function()
	currentSongFolder:ClearAllChildren()
	wait(0.5)
	local chosenSong = songs[math.random(1, #songs)]
	
	local songClone = chosenSong:Clone()
	songClone.Parent = songClone
	songClone:Play()
end)

And here is the code where I am trying to make it so when a new Sound is added, it will look to see if a Child was Added to the Current Song folder:

local starterGui = game:GetService("StarterGui")
local sliderBG = script.Parent

local slider = sliderBG:WaitForChild("Slider")
local currentSongFolder = starterGui.MusicGui:WaitForChild("CurrentSongFolder")
local currentSong = currentSongFolder:GetChildren()

local mouse = game.Players.LocalPlayer:GetMouse()

local snapAmount = 1
local pixelsFromEdge = 1

local movingSlider = false


slider.MouseButton1Down:Connect(function()

	movingSlider = true
end)

slider.MouseButton1Up:Connect(function()

	movingSlider = false
end)
mouse.Button1Up:Connect(function()

	movingSlider = false
end)


mouse.Move:Connect(function()

	if movingSlider then

		local xOffset = math.floor((mouse.X - sliderBG.AbsolutePosition.X) / snapAmount + 0.5) * snapAmount
		local xOffsetClamped = math.clamp(xOffset, pixelsFromEdge, sliderBG.AbsoluteSize.X - pixelsFromEdge)

		local sliderPosNew = UDim2.new(0, xOffsetClamped, slider.Position.Y)

		slider.Position = sliderPosNew

		local roundedAbsSize = math.floor(sliderBG.AbsoluteSize.X / snapAmount + 0.5) * snapAmount
		local roundedOffsetClamped = math.floor(xOffsetClamped / snapAmount + 0.5) * snapAmount

		local sliderValue = roundedOffsetClamped / roundedAbsSize

		currentSong.Volume = sliderValue
	end
end)

####Re-edited by JesseSONG!