Counting...

Amelia can count fairly well, but she always forgets to say the number 15...  So I knew this conversation was going to turn out funny from the get go:

Mia: Ana, you can play with that until I count to 15.  Then it is my turn.
Ana: Okay *sigh*
Mia: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24...
UH..Okay, my turn!

Why in the world did she pick 15?  Why not 3?