My for i,v in pairs loop wont work and I don't know why?

First of all, if you plan to ask lots of questions in ScriptingHelpers, it's best if you get used to wrap your code in between two sets of tilde symbols with this button, so that the code will be viewed like this:

for i, v in pairs(game.Workspace:GetChildren()) do if v:IsA("Model") then hum=v.Humanoid if hum==true then v.Humanoid:Remove() end end end

Second of all, reformat your code & utilize those whitespaces! They will make your code look more professional.

for i, v in pairs(game.Workspace:GetChildren()) do
    if v:IsA("Model") then
        hum=v.Humanoid
        if hum==true then
            v.Humanoid:Remove()
        end
    end
end

Look into the :FindFirstChild() method. It returns the child of its object given a string, or nil. An error is thrown due to models that do not have a Humanoid.

hum = v:FindFirstChild("Humanoid")
if hum then -- You absolutely do not need "== true", because "if" statements look at conditions that are true.

You've already defined Humanoid as hum. Why would you type more just to address it when you have a shorter alternative?

for i, v in pairs(workspace:GetChildren()) do
    if v:IsA("Model") then
        hum = v:FindFirstChild("Humanoid")
        if hum then
            hum:Destroy()
        end
    end
end

There's a more efficient way of doing this. Instead of looping through the WHOLE Workspace, why not loop through the players? That way you can use the Character property.

for i, Player in pairs(game.Players:GetPlayers()) do
    if Player.Character then
        hum = Player.Character:WaitForChild("Humanoid") -- Wait until `Humanoid` is not nil.
        if hum then
            hum:Destroy()
        end
    end
end

If the intended effect isn't achieved in this script, then try this instead (if you want to kill the characters).

for i, Player in pairs(game.Players:GetPlayers()) do
    if Player.Character then
        hum = Player.Character:WaitForChild("Humanoid")
        if hum then
            hum.Health = 0
        end
    end
end

But I don't know what you're trying to do, so don't use it if it doesn't apply to you. :P

Questions? Comments? Skepticism? Comment down below or PM!