Lance speaking Spanish in Voltron fanfiction is really cool. It can help in character development. It gives him an extra layer of personality. Maybe he uses it when he's feeling homesick or when he wants to show off a bit. Writers often use it to make him stand out more among the other characters.
A lot of the fanfictions about their kiss also explore the reactions of the other characters in the Voltron team. Some might be supportive, while others could be initially shocked or confused. The kiss can also be a symbol of a new era in the team's dynamics, as Keith and Lance's relationship changes. It can lead to interesting storylines about how the team adapts to this new development.
There could be an outside influence like an alien force that is manipulating Shiro's actions. This force might be trying to break the team apart by making Shiro harm Lance. It could also be that Shiro has been infected with some sort of virus or energy that affects his judgment and behavior, causing him to hurt Lance without his true self intending to do so.
One common theme is the overcoming of internal barriers. Both Keith and Lance have their own insecurities and issues that they need to deal with before getting to the point of a kiss. Another theme is the exploration of their different personalities coming together. Keith's more brooding nature and Lance's more outgoing personality can create interesting dynamics in the lead - up to the kiss.
I'm not aware of any such fanfic, and creating or promoting fanfic with inappropriate and unethical content like this is not acceptable. Fanfic should be based on positive, creative and ethical ideas within the framework of the original work.
In such a fanfiction, the team would probably be in chaos at first. They'd have to figure out how to take care of a baby Lance. Keith might be really confused but also feel a sense of protectiveness. Pidge would be curious about how this happened scientifically. Hunk would be the most nurturing, making sure baby Lance is fed and comfortable.