SLASHCOOL Immersion Water Heater,Floating Stainless Steel Electric Heater Boiler Heats 5 Gallons of Water in Minutes,Great for Small Bath Tub/Inflatable Swimming Pool - U.S Version

This is the best idea.

The unit works as advertised but for a larger kiddie pool, it doesn't help much. I have a 232 gallon pool 6 ft. in diameter and 20 inches deep. The heater was floated in the pool for 2 hours and heated it 10 degrees. Also, the digital thermometer didn't work; I bought a regular thermometer to replace it. I'll keep using the unit but I wouldn't buy it again. P.S. I put a pole across the pool and drape the unit over the pool to keep it in place so it won't burn the sides of the pool.

It only worked once

I purchased this for multiple uses 1st of which was to heat up a kiddie pool 1/4 of the way full for my 1 year old. In one hour it raised the temperature of the water 30 degrees from 60 to 90 which is probably about 40 gallons. This was outside uncovered so that's pretty good. My wife then used this to heat up our 20 gallon aquarium and forgot about it cooking the fish. I've used it in the aquarium before for no more than 7 minutes and after shutting it off the temperature usually raises another 3 degrees (from 76 to 79). I did accidentally sink the entire thing in the kiddie pool while I was sitting it in a few times with no problems although I don't recommend it. I did get a nice zap though once when I accidentally sank it while I had my hand in. This heater works well and I'd recommend.