Moving back up to 2 naps?

Married3.22.03

DD has been taking 1 long afternoon nap each day for months.  I don't even remember "dropping" her morning nap... it just sort of happened.  The one nap a day was fine because she was sleeping like 3-4 hrs.  In the last few weeks, she's been sleeping only like 1-2 hrs. during the same time slot, but also isn't taking other naps throughout the day either.  She gets so crabby when she's tired, and I really think she needs more sleep throughout the day.  (She sleeps about 12-13 hrs. at night, so that isn't the problem.)  Any ideas on how to build a second shorter nap in her day?  I've tried putting her down for nap earlier (when she gets crabby), but then she just sleeps her 1-2 hrs. and then won't nap the rest of the day... which means she's crabby earlier in the evening since that stretch of time is longer.

FSUSammy

DS has 1 nap a day for 1-2 hours. He gets crappy the closer we get to his bedtime. If I see that he is crabbier than usual I start his bedtime a little earlier and might put him down 30 minutes early. There are times when come 5pm he wants to go down because he is Mr. Crab so I'll put him down and I end up having to wake him up to start his bedtime routine because he is still sleeping. I only do that on his VERY off days, otherwise I really try to stick to the 1 nap a day thing.