local npcs = workspace:WaitForChild("NPCs")

local function setSpeed(humanoid)
    humanoid.WalkSpeed = 50
end

for _, descendant in ipairs(npcs:GetDescendants()) do
    if descendant:IsA("Humanoid") then
        setSpeed(descendant)
    end
end

npcs.DescendantAdded:Connect(
    function(descendant)
        if descendant:IsA("Humanoid") then
            setSpeed(descendant)
        end
    end
)