One challenge could be their different lifestyles. Lightning is often on the road racing, while Sally is more focused on the life in Radiator Springs. They'd need to figure out how to balance their time together and apart.
One possible fanfiction could be that Lightning McQueen decides to plan a grand wedding for Sally. He customizes his racing look to match Sally's elegant style for the big day. They hold the wedding in Radiator Springs, with all their friends like Mater and Doc Hudson (in spirit) helping out. The whole town is decorated with shiny lights and flowers.
Well, in a fanfiction, their baby could be a super - fast racer just like Lightning McQueen. Maybe it would inherit Sally's intelligence and McQueen's speed. It could grow up to be a legend in the racing world of Radiator Springs.
Well, one idea could be that they go on a journey to find the perfect place to raise their baby. They might encounter old friends along the way who offer different kinds of support and advice.
A fanfiction could revolve around the idea that an unexpected event leads to Lightning McQueen and Sally having a baby. Maybe there's a magical or strange occurrence in Radiator Springs. As they deal with this new situation, they learn a lot about themselves and their relationship. McQueen might have to learn to be more gentle and patient, and Sally would be the strong one guiding them through the early days of parenthood. It could show how their love grows even deeper with this new addition to their lives.
The baby could be really fast. Lightning McQueen is a racer, so speed genes might be passed on. It would be cute too, with Sally's colors perhaps blended with McQueen's.
Their friends would be really excited. Mater would probably be the most enthusiastic, constantly asking if he could take the baby for rides in his tow truck (in a very safe way, of course). Doc Hudson, if he were still around, would offer some wise words on raising a child. The other cars in Radiator Springs would bring gifts and offer to help with babysitting or any other needs.
One possibility could be a story where Lightning McQueen finally realizes his deep feelings for Sally during a big race event. Maybe he has a near - miss on the track and in that moment, he thinks of Sally. After the race, he finds her and they share a sweet, unexpected kiss.
The easiest way could be to check out the official websites of comic publishers. They might have it available for purchase or give information on where you can get it. Libraries could also be a possibility if they have a collection of comics.
They could have a race to celebrate the upcoming baby. But it's not a normal race. It's a race where they compete in a more gentle way, like who can reach a certain point first while carrying a small baby - like object. It's just for fun and to involve the whole town in their joy.