Is it possible to make all game parts a certain material?

Title, I've tried it and kinda works. The problem is, what if a model has more models inside it?

function optimize()
    local parts = workspace:GetChildren()

    for i,v in pairs(parts)do
        if v:IsA("Model") then
            local mParts = v:GetChildren()
            for i,v in pairs(mParts) do
                if v:IsA("BasePart") then
                    v.Material = Enum.Material.SmoothPlastic
                end
            end
        elseif v:IsA("BasePart") then
            v.Material = Enum.Material.SmoothPlastic
        end
    end
end