It’s the Friday Puzzle!

I was walking along the street and saw a woman playing with two children of different ages.  One of the children was a girl.  What are the chances that both children were girls?

As ever, please do NOT post your answers, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.