Problem with including 3D gnomes and goblins is making them distinct enough to not look like midgets while avoiding the uncanny valley problem. Frankly even big budget studios have this issue.
Probably why most 3D animators avoid them and use fairies instead since they don't need to worry about proportions.
As for the 1.2m elves, I don't think saying the age/lore matters if your art is going for full realism and their proportions are realistically prepubescent.
Gotta "elf it up"(whatever that means to you) or show why they are postpubescent, at least according to rule 7.