When the Booking Engine is configured to require a guest to enter the number of adults/children/infants on the inquiry screen (when requesting available rooms), they are then forced to enter it again on the Confirm screen where the system requests numbers of adults/children/infants to price per person rates properly.
Note that infants are counted as persons against the maximum persons per room. So, if a Room can occupy 4 people, and there are 3 adults and 1 child in a query, no infants will be able to 'fit' into the room, as the occupancy would then become 5. Also, if infant pricing is used, that infant does gets priced as an 'Extra Person' when pricing using an occupancy-based rate.
We usually recommend to avoid this issue by NOT showing the Number of Guests option on the Booking Engine (BE) screens at all. This means that availability is returned for your rooms, and how the guest will fit their party into the rooms is their choice when reviewing the rates and options.
Not only is this more convenient for your guests, but it has the added benefit of not limiting rooms based on their entry. For example, if you were to have rooms that only fit 3 people, and someone placed 4 adults into the number of adults/children/infants field on the inquiry screen, no availability would show, since none of your Room nor Types accepts 4 adults.
How to Turn the Number of Guests On and Off?
There is a setting in the Desktop Property Management System (Parameters | System Config | Online Config) 'Don't Show Number of Guests'. Turn this flag ON to avoid showing number of guests on the inquiry screen. Then do a Full Update.
Management Tool and MyPMS
In the Setup / Members Area, look for the Settings | Booking Engine Settings and choose the flag to "Don't prompt for number of guests" and then click the update button.
Watch how it works and play with it till it's right for your needs.