Kaitlin is a character from Animal Crossing: Wild World and Animal Crossing: City Folk. After the player first visits a town, or someone comes to their town, they will see a yellow cat. If it is Kaitlin, a mom who has lost her baby, she will guide the player to the town gate and report to them that she has lost her child. If the player travels to the town where she has lost her child, she will give you a gift.
"A mother and child who've gotten separated. After you've gone to visit a friend's town, you'll find either Kaitlin, the mom, or Katie, the wayward kitten, in your town. Both will tell you where they came from, and it's then your duty to travel to that town to reunite the family. Once you do, the player whose town Katie was in will get a letter of thanks and a present."