"I have a 12-month old son who I believe may be starting to transition to one nap. However, it is so inconsistent from day-to-day. One morning he will only sleep for 25 minutes or so, the next, two hours. Now, I've actually e-mailed you about napping problems before, but for the last three months, he has been consistently taking two naps that averaged about 1-1 1/2 hours. He still seems tired in the morning, so I hesitate to push him off for too long, but this really short morning nap is beginning to wreak havoc with the day. I guess my real question is, how do you typically begin the transition to one nap? Also, what happens if they don't consolidate their sleep, and end up only taking one short nap? Any suggestions on the whole single nap issue would be greatly appreciated."
Gah. Napping problems really mess with your head, don't they?
Consolidating from two to one nap seems to vary from kid to kid. It almost seems like the way boys' voices change in junior high--some go through weeks of cracking and screeching (a la Peter Brady), while others just go from high to low overnight (which my MIL claims my husband's did). My first son seemed to go from two naps to one in a matter of days (at 11 months), but plenty of kids spend weeks on the transition, as yours is.
I'll answer your second question first. In theory, when kids go from two to one nap, the new single nap is longer than either of the old naps, but shorter than their combined time was. So if he used to take a morning 90-minute nap and an afternoon 1-hour nap, the new nap will probably be around 90-minutes to 2 hours. In practice, this could happen, or the new nap could be shorter (1 hour to 90 minutes) and he could increase his nighttime sleep a little. As he grows older he needs less sleep. According to the chart in the No-Cry Sleep Solution, a 9-month-old needs 14 total hours of sleep (with 2 naps totalling 2.5-4 hours), a 12-month-old needs 13-14 total hours of sleep (with 1-2 naps totalling 2-3 hours), and 2-year-old needs 13 total hours of sleep (with 1 nap of 1-2 hours). So he's starting to need slightly less sleep during the course of the day anyway. But he'll still probably end up getting basically the same total time over a 24-hour period, just divided up slightly differently.
About trying to transition to one nap from two: You have to look at what kind of napper he is. Is he the kind of kid who will go down for a nap when you set the stage and go through the routine of putting him down? Or is he the kind of kid who won't nap unless he's tired, no matter how many hoops you jump through?
If he's the first kind (who will go down when you go through the naptime routine), I'd suggest doing a 1-2-month plan to get him from two naps to one. Start pushing his normal first naptime back by 10 minutes every few days. Let him sleep as long as he wants, but then cut his second nap shorter and shorter little by little. Eventually they'll meet in the middle and he'll be going down later and sleeping longer and not taking a second nap at all. It's not going to be linear, and you'll still have crappy days, but at least you'll feel like you're heading somewhere.
If he'sthe kind of kid who will only nap when he's sleepy, change the rhythm of his day. Instead of doing winding-down activities right before his normal first nap, start engaging him in a lot of physical activity. If he's running around like a fool at the time he'd normally be going down for his first nap, not only will he start napping later (because you can't run and sleep at the same time), but when he does go down for a nap he'll probably sleep longer just from being so physically tired. Of course this will be easier in the summer when you can be outside running around, but maybe you can schedule outside errands during his normal naptime that allow him the ability to run now while it's still cold and nasty outside. If his first nap is later and lasts longer, eventually it'll turn into his only nap.
Of course you could also just wait it out and he'll eventually go to one nap on his own. But it sounds like it's really bugging you, so you might as well try to do something about it, even if it doesn't work right away. Just know that if you start to get too annoyed trying to shift his nap schedule, you can just take a breather and do nothing for awhile and he'll eventually settle into one nap a day.