How to make this script spawn 20 rocks, and then spawn rocks back to 20 when rocks destroyed?

So, ive got this script that is supposed to spawn 20 rocks inside the given area, and then only spawn more when there are less than 20, all the way back up to 20. i get no errors, but it doesnt spawn anything. a

local function GenerateRocks()
    for i = 1, 20 do
        local numberofrocks = workspace.Rocks:GetChildren()
        local RockClone = game.ReplicatedStorage.Rock1:Clone()
        if #numberofrocks == 20 then
            break

        else
            RockClone.Parent = workspace.Rocks

            local RandomX = math.random(-86.341, -71.519)
            local RandomZ = math.random(136.349, 143.938)

            RockClone.Position = Vector3.new(RandomX, 2, RandomZ)
        end
    end 
end
GenerateRocks()