Pants, Pantalón vs. Pantalones

Rosetta Stone
1-1-9
Clothing with added material

Pantalón vs. pantalones

The girl wears pants is: La niña lleva pantalón. La niña lleva pantalones.

The girls wear pants is  Las niñas llevan pantalón. Las niñas llevan pantalones.

Both pantalón and pantalones seem to be correct and can be used interchangeably, according to some sources. However, more sources say that pantalones is more often used.

Although it looks like this may be one of those grammar issues for native spanish speakers too, considering there are spanish articles on this:

http://blog.lengua-e.com/2008/pantalon-o-pantalones/

I am marking the above site here until I can translate it all and figure out what the right answer is. :-)

Also of note:

Whether it's a singular or plural set of people wearing pants, both the singular and plural of pants seems to be okay to use.  Ex: Las mujeres llevan pantalón.

I have also seen 'pantalón' and 'pantalones' both with and without an article (el, los, un, or unos), following llevar. I am unsure if this is preference or if there is a rule I do not yet know.

Other bottoms:
calzones - shorts (Latin America and Mexico)
pantalones cortos (m) - shorts, a pair of shorts
calzoncillos  - underpants
vaqueros(m) - denim trousers/jeans
jeans (m) - jeans (Mexican slang). This seems to be used with a plural article for a singular pair of jeans.
jeans ceñidos or vaquero ajustado - skinny jeans
falda (f) - skirt