mix up
n.-
To confuse the identities of (two or more objects); to mistake (one object for another);
as, at the family gathering he .mixed up his two nieces, to their great amusement -
To mix together; -- usually implying a mistake, whether done intentionally or unintentionally;
as, the .mixed up this year's receipts with last year's, and it took hours to find the right ones
