With the producer of the ''Avatar'' sequel, John Landau, having confirmed in interviews over the last few weeks that the forthcoming 'Avatar' sequels will complete the characters arcs for the two main characters from the first movie, speculation has been rife regarding what will occur to Jake and Neytiri in the immediate follow-up. There are all manner of possibilities, with some individuals even believing that some of the Na'vi will travel to Earth in some capacity.
But one of the storylines that I really see as being both possible and natural is for the couple to produce a child. There are several reasons why this would work well in an 'Avatar' sequel. Firstly, as much as a story about a war between two tribal creatures, namely human-beings and Na'vi, the first 'Avatar' film was quite obviously a story about these two characters falling in love. In this respect, the film had similarities with the first James Cameron directed 'Terminator' movie, in which Sarah Connor and Kyle Reese fall in love before the background of events of huge significance to the entire human race.
Secondly, if Jake and Neytiri produce a child then this leaves the door open to have almost a new generation of 'Avatar' movies that focus on this individual, and the characters that (s)he comes into contact with. It has already been confirmed that there will be two more 'Avatar' movies at least, at which point the Jake and Neytiri story will have been concluded, but rumours abound that more 'Avatar' movies could follow that in the future, with the studio keen to exploit the seemingly limitless possibilities of the Pandora universe, both in storytelling and commercial terms.
Again, there is a precedent for this in the 'Terminator' movies, with the pregnancy of Sarah Connor from the first 'Terminator' movie leading to the plot for 'Terminator 2: Judgment Day' in which the now grown up John Connor is targeted for termination by a cyborg from the future. Although James Cameron turned his back on the 'Terminator' franchise after the second film, sources close to him have indicated that he considers the 'Avatar' movies more of a labour of love. And given his taste for 3D film, the technologies that produce it are constantly developing, and Cameron may consider in the future that he can deliver ever more immersive and visually impressive leaps into the Pandora universe in the future.
Thus, I think Jake and Neytiri having a child together is a natural storyline for the sequel, and one that we could easily see on the big screen.