A woman in Michigan won $78,000 in the lottery last week . . . because she forgot how old one of her kids was, and played the wrong number.

Your mom would never forget your birthday, right?  Well, a mom in Michigan recently forgot how old one of her kids was, but it was a GOOD thing she did.

Antoinette Ousley lives outside Detroit.  And she won a pretty sizable chunk of money in the lottery this month . . . because she screwed up her kid's age.

Whenever she buys a ticket, she comes up with the numbers by using a combination of her kids' ages and birth dates.

And one of her kids recently turned 20, but she forgot.

So she used 19 as one of her numbers last week . . . matched all five numbers in the drawing . . . and won 78 GRAND.

Her other kids are younger, and still live at home.  So she's planning to use the money for a down payment on a new house.