Return Players Health back to 100 when god?

Your question is very confusing, but I'll do my best to give an answer! =)

I'm assuming you're making an anti-hack where when the player's health goes to god, then it'll reset the player's health. Instead of checking for god, I feel it would be more efficient to check for anything over the max amount of health for your game.

local maxHealth = 120 -- Used to define the max amount of health for players.
local player = game.Players.LocalPlayer --Can only be used in local scripts
player.CharacterAdded:connect(char) --When the character is added
	local humanoid = char:WaitForChild('Humanoid') --Wait for Humanoid
	humanoid.HealthChanged:connect(function() --When the health is changed
		if humanoid.Health > maxHealth then --Is it higher than the max health?
			humanoid.Health = maxHealth --Change to max health
		end
	end)
end)

This would be for a game that does not have FilteringEnabled enabled. However if you do, you could run some remote events.

Local

local maxHealth = 120 -- Used to define the max amount of health for players.
local player = game.Players.LocalPlayer --Can only be used in local scripts
local event = game.ReplicatedStorage:WaitForChild('HealthChanged') --Requires RemoteEvent in Replicated Storage called HealthChanged
player.CharacterAdded:connect(char) --When the character is added
	local humanoid = char:WaitForChild('Humanoid') --Wait for Humanoid
	humanoid.HealthChanged:connect(function() --When the humanoid's health changes
		if humanoid.Health > maxHealth then --Check for if it's higher than the maxHealth
			event:FireServer(humanoid) --Fire the server with the humanoid
		end
	end)
end)

Server

local maxHealth = 120 -- Used to define the max amount of health for players.
local event = game.ReplicatedStorage:WaitForChild('HealthChanged') --Grabs event
event.OnServerEvent:connect(function(player, humanoid) --When the event is triggered by client, grab the player and humanoid
	humanoid.Health = maxHealth --Change the health to maxHealth
end)

If the script is too confusing to read because of the comments I left, you can click the Script with Less than and Greater than arrows at the top right, whenever you hover over the script.

Now to talk about your script! =)

local MaxHealth = 120

game.Workspace.ChildAdded:connect(function(Child) --Bit strange to do. But I understand your usage of it.
 local Humanoid = Child:FindFirstChild("Humanoid")
 local Player = game.Players:FindFirstChild(Child.Name)

 if Humanoid then
  Humanoid.Changed:connect(function() --This will check for every single change in the humanoid, from if they're walking, to jumping, to falling, to anything.
   if Player and Humanoid.MaxHealth == math.huge then --I would do greater than your maxhealth, as some hackers will just change their health to right under god mode =)
    Player:Kick("You have lost connection to the game") 
   elseif Player and Humanoid.MaxHealth > MaxHealth and Humanoid.MaxHealth < 9e9 then --Excess ElseIf
    Player:Kick("You have lost connection to the game")
   elseif Player and Humanoid.MaxHealth == 0 and Humanoid.Health > 0--Excess ElseIf
    then Player:Kick("You have lost connection to the game")
   end
  end)
 end
end)

I hope you understand, and that the knowledge provided can help you in the future =).

PS: FilteringEnabled will catch a majority of hackers, unless they are highly experienced, and even then, anything you do they will bypass somehow.