Why does it say that leaderstats is not a valid member? I used waitforchild too.

Below is the script that's erroring.

local Players = game:GetService("Players")

local kickCommand = "!kick "

local function onOwnerChatted(player, message)
	if message:sub(1, kickCommand:len()):lower() == kickCommand:lower() then
		local name = message:sub(kickCommand:len() + 1)
		local playerToKick = Players:FindFirstChild(name)
		if playerToKick then
			playerToKick:Kick("Our moderators have determined that your behavior at SF Nuclear Lab has been in violation of our rules. Therefore, you are kicked from this game.")
		else
			
		end
	end
end

local function onPlayerAdded(player)
	if player.leaderstats.GVC2YDJ5.Value >= 1 then
		player.Chatted:Connect(function (...)
			onOwnerChatted(player, ...)
		end)
	end
end

for _, player in pairs(Players:GetPlayers()) do
	onPlayerAdded(player)
end
Players.PlayerAdded:Connect(onPlayerAdded)

Below is the leaderstats script.

local Players = game:GetService("Players")
local DataStoreService = game:GetService("DataStoreService")
local TestDataStore = DataStoreService:GetDataStore("emp43")

local data = {
	["22XQ3SGH"] = 0,
	["XTSAT8B7"] = 0,
	["RVESMDXG"] = 0,
	["8YHCNKMD"] = 0,
	["D4VWKQF7"] = 0,
	["ENB78YBQ"] = 0,
	["GVC2YDJ5"] = 0,
	["TKBRVCBQ"] = 0,
	["6TU53T5F"] = 0,
	["A79QBG5C"] = 0
}

Players.PlayerAdded:Connect(function(Player)
	local DataFromStore = nil

	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = Player

	for name, value in pairs(data) do
		local new = Instance.new("NumberValue")
		new.Name = name
		new.Value = value
		new.Parent = leaderstats
	end

	local s, e = pcall(function()
		DataFromStore = TestDataStore:GetAsync("uid-" .. Player.UserId)
	end)

	if s then
		print("Getting Data For: " .. Player.Name)
		if DataFromStore then
			for name, value in pairs(DataFromStore) do
				Player.leaderstats[name].Value = value
			end
			print("Data Loaded For: " .. Player.Name)
		else
			print("Created New Data For: " .. Player.Name)
		end
	else 
		warn("Error Getting Data For: " .. Player.Name)
	end
	
	-- Check if banned.
	
	--if Player:WaitForChild("leaderstats").ENB78YBQ.Value >= 1 then
		--Player:Kick("Our moderators have determined that your behavior at SF Nuclear Lab has been in violation of our rules. Therefore, you are banned from this game.")
	--end
end)

Players.PlayerRemoving:Connect(function(Player)
	local DataForStore = {}

	for name, value in pairs(Player.leaderstats:GetChildren()) do
		DataForStore[value.Name] = value.Value
	end

	local success = pcall(TestDataStore.SetAsync, TestDataStore, "uid-" .. Player.UserId, DataForStore)

	if success then
		print("Successfully Saved Data For: " .. Player.Name)
	end
end)

game:BindToClose(function()
	for _, v in pairs(game.Players:GetPlayers()) do
		local success, errormessage = pcall(function()
			TestDataStore:SetAsync(v.UserId, data) -- define the data, since it's in a different scope
		end) 
	end
end)

First off it should be a serversided script within server script service. You should remove the waitforchild considering they are not very good in serversided scripts. Try this.

local Players = game:GetService("Players")
local DataStoreService = game:GetService("DataStoreService")
local TestDataStore = DataStoreService:GetDataStore("emp43")

local data = {
    ["22XQ3SGH"] = 0,
    ["XTSAT8B7"] = 0,
    ["RVESMDXG"] = 0,
    ["8YHCNKMD"] = 0,
    ["D4VWKQF7"] = 0,
    ["ENB78YBQ"] = 0,
    ["GVC2YDJ5"] = 0,
    ["TKBRVCBQ"] = 0,
    ["6TU53T5F"] = 0,
    ["A79QBG5C"] = 0
}

Players.PlayerAdded:Connect(function(Player)
    local DataFromStore = nil

    local leaderstats = Instance.new("Folder", Player) --Parent it within the instance here not there.
    leaderstats.Name = "leaderstats"

    for name, value in pairs(data) do
        local new = Instance.new("NumberValue", leaderstats) --Same thing here.
        new.Name = name
        new.Value = value
    end

    local s, e = pcall(function()
        DataFromStore = TestDataStore:GetAsync("uid-" .. Player.UserId)
    end)

    if s then
        print("Getting Data For: " .. Player.Name)
        if DataFromStore then
            for name, value in pairs(DataFromStore) do
                Player.leaderstats[name].Value = value
            end
            print("Data Loaded For: " .. Player.Name)
        else
            print("Created New Data For: " .. Player.Name)
        end
    else 
        warn("Error Getting Data For: " .. Player.Name)
    end

    -- Check if banned.

   if Player.leaderstats.ENB78YBQ.Value >= 1 then --Assuming your having the problem here. I will fix it up.
        Player:Kick("Our moderators have determined that your behavior at SF Nuclear Lab has been in violation of our rules. Therefore, you are banned from this game.")
   end
end)

Players.PlayerRemoving:Connect(function(Player)
    local DataForStore = {}

    for name, value in pairs(Player.leaderstats:GetChildren()) do
        DataForStore[value.Name] = value.Value
    end

    local success = pcall(TestDataStore.SetAsync, TestDataStore, "uid-" .. Player.UserId, DataForStore)

    if success then
        print("Successfully Saved Data For: " .. Player.Name)
    end
end)

game:BindToClose(function()
    for _, v in pairs(game.Players:GetPlayers()) do
        local success, errormessage = pcall(function()
            TestDataStore:SetAsync(v.UserId, data) -- define the data, since it's in a different scope
        end) 
    end
end)