#Problems
There are a few errors in your code.. i'll walk you through them.
- The
GetChildren function returns a table of the specified object's descendants. The function you're looking for is the FindFirstChild function.
- You have 2 contradicting if statements. You should omit the second one from your code
- When you reference the 'FlyGUI', you should reference the actual object rather than a string representing the object. It saves you the need to search for the item.
#####note: remember to use variables to keep your code clean and readable!
#Code
local player = game.Players.LocalPlayer
local FlyGUI = game.ReplicatedStorage.FlyGui
if not player.PlayerGui:FindFirstChild(FlyGUI.Name) then
FlyGUI:Clone().Parent = player.PlayerGui
end