I'll pile on for good measure.
Six months out is generally a sweet spot, as the low-cost airlines (Southwest, JetBlue, etc) release their schedule and pricing about this time. The legacy airlines (Delta, American, United) will adjust their prices to bring them in range.
As mentioned, the legacy airlines generally release their schedule and initial pricing eleven months out, so you can get an idea of what the flights may cost.
I recommend you use
Hipmunk or the
ITA Matrix to have a look at prices, since these tools are not brokers, so they don;t make money from the airlines like Expedia, Orbitz, Priceline, etc. Both ITA and Hipmunk use the same tool, however TA Matrix site is more advanced and Hipmunk has a link directly to the airline's booking site, which is very useful.
Remember the general rule of booking flights:
Determine what price threshold would be comfortable for you and your family before you go searching. have a look at the general price for that time of year via the sites mentioned above. Adjust your price point accordingly.
Finally, keep and eye on airline prices. When you find a price you'd be comfortable with paying, book the flight with no regrets. Prices can go up and down, and will usually fluctuate during the course of the year, driving you mad to lock down the "ultimate lowest price ever".
Have fun and good luck!
Oh, and stay away from Spirit. Low low prices, but not really as they charge for things other airlines provide for free.