Ok, I'll give a few more details. LOL Alaska air typically offers kids fly free from early Jan-until mid June. Sometimes United air offers it as well. Jan- April 26th (or so) Disney usually offers a special on tickets as well. Last year it was kids play free with full price adults or if you just needed adult tickets they were at the kids price. This year it was every one at the kids price. In the fall they will offer 4th night free at some of the hotels (on site and off).
The number of kids fly free tickets on any flight are limited. And, to get the kids fly free price you have to pay full fare for the adult tickets. Sometimes the kids fly free is a great deal, other times not. For our April trip, from Seattle to Long Beach it was about $550 for all 4 of us. We booked about 4 1/2 months before the trip to get the flights we wanted at the best price. If you wait until the last minute its going to cost more. The cheaper seats and kids fly free may be sold out on the flights you want. Sometimes to get the best deal you have to check other airports or change dates by a day or so.
From mid-June to mid-Sept you probably will not find many discounts or specials. From mid-Sept (after Labor day) thru the end of the year you can typically get the 4th night free.