The slimy stuff is algae. If you plan on leaving water in the pool, you have to add chlorine. Without it bacteria can grow to dangerous levels for swimmers and it will become a breeding ground for mosquitos. Chlorine is only sold in large amounts, which wouldn't be very cost effective for a kiddie pool. You can find small chlorine floaters made for spas, or maybe you could get a bag of chlorine shock and use little bits of it. You'll need chemicals to test the chlorine and pH levels, too, otherwise the water can be very irritating to the skin. I have an old test kit from last season that you can have if you're willing to come get it - I live in Mesquite. I can also give you a few chlorine tablets. But without circulation like you get from a pool filter, I would still think you'd need to empty it every couple of weeks.