baby koi over winter

Question
I was shocked to see baby koi in our pond. info: The pond is 23x18 and 8' deep. Waterfall is 13' at the head for oxygenation plus an nice sized airstone and pump. Have an undergravel filter under 6" of pea gravel. I have never cared for koi so young and they seem to be thriving.  They are 2" up to 4.5".  My question is will they winter alright?  We are in Washington state northeast of Seattle about an hour.  So, we do get cold weather and some snow on a sporatic basis.  Do I need to think about a heater?  In another week or so I will begin feeding the koi low protein foods to clean them out.  What about the babies?  I am reading what I can find.  Can you help me?

Answer
Hi Bug:  Treat the babies as you would the adults... Move the pond filter to about a foot below the surface of the pond or get a pump that will break the surface to keep the water from freezing solid.  Moving the pump to the surface will recycle the cold surface water and not the warmer water on the bottom of the pond. You can also get a de-icer too.  You Koi must love your pond... keep me posted.... dave