The little three year old girl in my class came to the hospital to visit her mom and was thrilled with her baby brother. She kept calling him by her three week old cousin's name, no matter how many times her mama corrected her. When he came home the little girl was excited to have (her cousin) there and kept asking where her aunt was. She didn't understand even when she was told, "He's ours."
Her mom removed the baby's diaper, and he peed all over the little girl's foot. Mama said, "Get me a diaper, quick!" The little girl said, "Get my foot cleaned. Quick! This is gross. Take him back to auntie."
Mom invited auntie over one day so the little girl could understand. When she came in and saw both babies lying there, she yelled in disgust, "Now what are we going to do with TWO of them?!"
Mom explained one was theirs and one was auntie's. Six weeks later she realized her brother was there to stay. She's still not real thrilled.