It's always a gamble. I typically buy tickets 3-4 months in advance for the best fares. Anything 6 months or beyond tends to be more expensive. However, if you've got specific times and days to travel, don't wait too long. You don't want to get stuck on a flight with multiple stops just to get the cheapest fare. I've found that when I've held out too long to save a few bucks, I might have gotten a cheaper flight, but the travel time (redeye, for example) was not worth it with a little one. Check multiple online sites, ask some travel agents, and you should be OK. Good luck!