Toddler with bald spot

I took my 2 and a half year old to get her first hair cut and while there the hairdresser pointed out to me that my daughter has a bald spot that's between the size of a quarter and a half dollar.  Does anyone know what it could be, whether it would be something that's normal or something that I should worry about?  She said about bringing it up at her next well dr. appointment, but that's months away and I'm a worrier by nature, so I'll be worrying for the next couple of months.  Any ideas or help will be greatly appreciated.  Thank you!!