Why is this ChildAdded Event not Working?

I'm making a custom Leaderboard GUI. ChildAdded event is not firing. Output reads 1. Neither 2 or 3 appear.

local Player = game:GetService('Players').LocalPlayer
local PlayerGui = Player:WaitForChild('PlayerGui')

local Frame = PlayerGui.Leaderboard.Frame


print(1)
local function IncreaseFrame()
    print(2)
    if Frame.Size.Y.Offset < 245 then
        print(3)
        Frame.Size.Y.Offset = Frame.Size.Y.Offset + 20
    end
end


Frame.ChildAdded:Connect(IncreaseFrame)

Here is the code which adds a TextLabel to Frame on player join (same script):

local TL = Instance.new('TextLabel')
TL.Name = Player.Name
TL.Text = Player.Name
TL.AnchorPoint = Vector2.new(0.5,0)
TL.Position = Frame.User.Position
TL.Size = Frame.User.Size
TL.TextSize = 16
TL.TextStrokeTransparency = 0.5
TL.Font = Enum.Font.GothamSemibold
TL.BackgroundTransparency = 1
TL.TextColor3 = Color3.fromRGB(255,255,255)
TL.TextXAlignment = Enum.TextXAlignment.Left

TL.Parent = Frame -- THIS SHOULD FIRE CHILDADDED