Is there special pricing for children on shore excursions?

In most cases, yes.  When an operator offers a child price, the special pricing will be valid for children ages 4 – 12 years old.  Infants 3 and under are carried free of charge, subject to them not occupying a seat. 

Note that tours that include air transportation (seaplanes, helicopters, etc) all guests ages 2 & up will require a paid seat.