Well I know they heat the pools there so the water will be warm, but its really the the wind/if there a cold-front comes. I don't think I would want to swim, but I live here and I'm used to swimming in nice weather. I don't think that you would want to take a 18 month old but its really up to you and what you think is cold. I would play it by ear and if its to cold when you get there, then you have extra spending money.