Losing my marbles

Little Sara always likes to play with my collection of marbles.
As soon as she got home this summer, she said: Where are the colourful glass marbles that I like so much?
At first I didn't understand which ones she was referring to, but finally I found the jar with those marbles and gave it to her.
I am afraid that one day she will ask me about them and I will have to admit that I have lost my marbles, or my head ...