Maybe Harry tries to feed the baby cousin some magical baby food. He could make funny faces to get the baby to open their mouth and eat. It would be really adorable to see the baby's reaction to the new flavors.
In the fanfiction, it might be that Harry has to put the baby cousin to sleep. He could sing a soft lullaby, perhaps a wizarding world lullaby that has a gentle magic to it. He rocks the baby gently in his arms until the baby dozes off, with a little smile on their face.
Well, clearly Harry is one of the main characters as he is the one taking care of the baby cousin. The baby cousin is also a main character, even if it's a young and not fully developed character yet.
One heartwarming scenario could be Magnus using his magic to create a beautiful, enchanted nursery for baby Harry. He could fill it with floating toys and a crib that rocks itself gently. Another might be Magnus cooking special baby food for Harry with a touch of magic to make it extra delicious and nutritious. Maybe he'd also read him magical bedtime stories that bring the pictures to life on the walls of the room.
In such fanfiction, McCoy might struggle with understanding Spock's unique Vulcan needs as a baby. For example, he could be puzzled by Spock's early telepathic abilities or his different dietary requirements compared to human babies.
One interesting scenario could be Poseidon using his powers to create a mini - underwater world for baby Percy to explore safely. He might make colorful fish swim around Percy and gentle sea currents act like a cradle.
A heartwarming moment could be when Harry takes the baby out for a walk. He pushes the stroller carefully, talking to the baby about all the things they see around them, like the colorful flowers and the friendly squirrels. And at night, when the baby has a nightmare and Harry stays up all night comforting it. He rocks the baby gently and whispers soothing words until the baby calms down and falls back asleep.
One common scenario is Snape protecting Harry from the Dark Arts attacks within Hogwarts. Another could be Snape helping Harry with his studies privately, especially in potions where Snape is an expert.
Maybe it's the child of one of his friends or allies. For example, it could be the baby of Ron and Hermione. Harry would then be taking care of the baby out of loyalty and friendship.
One challenge could be getting Hermione to eat. Babies can be picky eaters, and in the wizarding world, there might be special potions or foods that Hermione needs but doesn't like. Another challenge is keeping her safe from magical accidents. With all the magic around, a simple spell could go wrong and put Hermione in danger.
One possible plot could be that Harry discovers a time - traveling accident has brought baby Snape to his present. Harry, being the kind - hearted person he is, takes it upon himself to care for the baby. He has to figure out how to feed the baby, keep him clean and comfortable. Maybe he also has to protect baby Snape from any threats in the wizarding world that might target Snape even as a baby.
In this fanfiction, perhaps Harry could struggle at first with the basic tasks like feeding and changing the baby. He might make mistakes but learn quickly.