Our 13 month old has always been a pretty good sleeper, sleeping straight through 7-7 ish for six months. She had a cold around the time when the clocks went back and has been waking between 5-5.30 ever since. Some days have been as early as 4am, plus there are often several short night wakings. We are creeping about very quietly and going to bed at 9-9.30 to try and deal with it. The worst we had was on Saturday where she woke every hour from midnight and was up for the day at 4am. The last few nights have been better in that she is not waking up in the night and although waking at 5.15, she has stayed in her cot with low level grumbling until about 5.45/6am, where we get up once she starts fully crying.
She is Still going to bed very easily at 7pm and napping well twice in the day. We don't have set nap times, but I have tried to keep her up until at least 8am so that she's not using the morning nap to catch up on night time sleep. She had one long nap from 12.30-2.30 the other day, but that didn't make any difference.
I don't know if she's got some teeth coming through, if it's a development thing, or just a phase or if this is her new routine now.
She is an extremely active child, has been walking for three months already so its not that