A/N: I've adopted this story from Really Big Hat, because, unfortunately, she's not continuing her Phineas and Ferb stories because she's moving on to KND stories. I'll post what she wrote, and then continue it for myself.
DISCLAIMER: I don't even own the idea for this story, let alone Phineas and Ferb.
The Flynn household was at the Super Duper Mega Super Store when Linda Flynn was having trouble managing her three kids, Candace Flynn, and the two year-old twins, Alexandra and Phineas Flynn.
"Mommy, I need to use the restroom!" whined Candace who was tugging on her mother's shirt.
"Hold on Candace." Linda replied setting Alexandra and Phineas down on a table for a quick second. "Marcus!" she called to her husband who was watching a football game on the display T.V.'s
"Yea?" he called back.
"Watch Alex and Phineas while take Candace to use the restroom."
While Linda took Candace to the restroom, Marcus was still watching T.V., not caring that little Alexandra was crawling off the table and in a near by cart. The cart was filled with clothes which broke Alex's fall.
Little Phineas knew something was wrong and started crying. "Shut up ya little brat!" shouted Marcus who continued to watch the game.
More clothes were piled into the cart and carried Alex off. Phineas continued to cry as he watched his sister leave.
As Linda and Candace came back, Alex was far gone. She heard her son crying and quickly rushed to him. Phineas, what's wrong?" she asked, picking him up. Then something hit her. "Where's Alex?" she asked the distracted Marcus.
"Huh? Oh, right there with Phin." He said turning around. "Hey, where'd she go?"
Linda was furious. "I don't know Marcus! I left YOU in charge of her! Man you are so stupid! I don't want to see you again!" Linda yelled, putting Phineas and Candace in the shopping cart and rushed to the check out area.
Marcus fallowed her, trying to convince her not to leave him. "Linda please, I will find her." he said, lying. He didn't give a flying pancake if he found Alex or not. He didn't even want the kids in the first place.
"Marcus, you and I both know you don't care." Linda said checking out all of her things quickly at the self checkout. After she was finished, she rushed out the door and quickly loaded all of her things in the car and put Phineas and Candace in their car seats. Linda got into her seat and locked the doors before Marcus could even reach the car. Linda drove away, leaving Marcus in a trail of dust.
He sighed. "Oh Flynn, why did you have to mess it up again?" he asked, giving himself a face palm and walked back into the store.
When he walked back inside, he saw a little two year-old girl with red hair in a young woman in her late 20s' shopping cart. Could that be…, no it couldn't. Marcus thought and walked back to the T.V.'s.