Script doesn't seem to be working for anything in StarterGui?

When the player's character sits on a chair, some text labels, text buttons, and images show up for a decision to go fast or slow, in a folder in ScreenGui called Decision. The labels are set to visible = false but when I sit on a chair, no errors show in the output but the labels don't become visible. Any help? Here's the script (It's in StarterCharacterScripts)

local fast = game.StarterGui.ScreenGui.Decision.Fast
local slow = game.StarterGui.ScreenGui.Decision.Slow
local hum = script.Parent.Humanoid
hum:GetPropertyChangedSignal("Sit"):Connect(function(sit)

    if hum["Sit"] == true then
        for _, child in pairs(game.StarterGui.ScreenGui.Decision:GetChildren()) do
            child.Visible = true
        end

        fast.Activated:Connect(fastt)
        slow.Activated:Connect(sloww)
    end

    if hum["Sit"] == false then
        for _, child in pairs(game.StarterGui.ScreenGui.Decision:GetChildren()) do
            child.Visible = false
        end
    end

end)

function fastt()
    hum.WalkSpeed = 30
end

function sloww()
    hum.WalkSpeed = 1
end