My kids somehow have perfect pitch. They hear a microwave beep and can say "that's b-flat". They say it's the same as looking at some shoes and naming the color

My kids somehow have perfect pitch. They hear a microwave beep and can say "that's b-flat". They say it's the same as looking at some shoes and naming the color. From everything we've read, that skill had to be established in them when they were pretty young. The only musical experience they had at that age was my old Casio SK-1 that I gave to them when they were three or four. Maybe they learned notes from playing with that? I don't think they knew the notes had names until they were older and started taking music lessons.