Maybe the story could focus on the daily challenges of raising a baby in a different world or time period. If it's a fantasy setting, they might have to deal with magical creatures while taking care of the baby. They could have to find special food for the baby that only grows in enchanted forests.
Often, the parents of the baby are main characters. They could be named characters from the original source material related to 'Summers' if it's a fanfic based on an existing franchise. For example, if it's related to the X - Men and the Summers family, Cyclops and Jean Grey might be the parents.
One interesting plot could be Naruto discovers a forbidden jutsu that allows him to raise the dead accidentally. He then has to deal with the moral implications of bringing back his fallen comrades, like Sasuke's family. Another idea is that the enemies get hold of the same jutsu and raise powerful dead shinobi against the Hidden Leaf.
One idea could be that baby Mario and baby Luigi get lost in a magical forest filled with strange creatures. They have to use their baby wits and little jumps to get through obstacles and find their way back home. Maybe they befriend a little fairy who guides them part of the way.
One idea could be that Baby Mario and Baby Peach go on a magical adventure through the Mushroom Kingdom, encountering new and strange creatures along the way. They might have to work together to solve puzzles to reach a special power - up that can save the kingdom from a new threat.
Perhaps a story where the baby malachite is a special kind of malachite that is prophesied to bring great change to its realm. Some might want to protect it while others might see it as a threat. The baby malachite then has to deal with all these different attitudes towards it. It could also be about its relationship with a wise old mentor who teaches it about its heritage and the responsibilities that come with its powers.
One idea could be a story where Baby Nightwing is discovered by the Justice League. They have to figure out how to take care of him while also protecting him from villains who might want to use him. Another could be a time - travel story where an older hero goes back in time and meets Baby Nightwing, and has to ensure his safety so that the future doesn't change.
One idea could be a story where the baby Mikaelson has unique powers that start to manifest at a very young age. Maybe they can communicate with spirits, and this leads to all sorts of adventures as the family tries to protect the baby from those who might want to use their powers.
One plot idea could be that Baby takes over Goku's body and tries to use his power to conquer the universe in a more subtle way. He might pretend to be Goku at first and manipulate his friends into doing his bidding without realizing it.
One idea could be exploring what would happen if Maleficent had a baby with a human. Maybe the baby would have a unique blend of magical and human traits, and the story could follow how the baby is accepted or rejected in both the human and magical worlds.
One idea could be a story where the baby in the 'baby project' has some sort of special power that the characters have to figure out how to manage. Maybe the baby can communicate telepathically and it leads to all sorts of comical and heartwarming situations as the characters try to understand what the baby wants.