Frankly, it doesn't sound like you need any help keeping them out. The kids asked once, when it was under construction, when they could swim. Doesn't sound to me like they are there everyday asking, or trying to climb the fence. If your mother is concerned that the new pool might be too tempting for a 5 yr old and/or a 2 yr old to resist, she better finish that fence, pronto. Whether your city ordinances require a fence or not, she needs to have it fully fenced for her own peace of mind. ANYBODY could drown in 4ft of water, in the right (or wrong, I should say) circumstances.