It's a complicated issue, but maximum occupancy is the total number of people in the room. Infants, newborns, children, and teenagers all count towards the maximum occupancy, regardless of age or size.

As for extra person charges, most hotels do not levy them on guests of a certain age (which varies by location unfortunately). I would think 14 would be considered a child, but the hotel front desk can tell you for sure. The exceptions may be resorts or certain packages (like all-inclusive packages).

The proper reservation proceedure would be to select four guests for the room. If you want, you can put in a note on step five of six that says the third and fourth guests are under 14 years of age.