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What did you notice if anything about LO's nightime sleep when this happened? DS usually naps a total of 3-3.5 hours total of daytime sleep and it looks like he's trying to transition to one nap. I can't imagine what he would do it he only slept like 2 hours during the day in one nap. Did your LO sleep more or less at night after the transition to one nap?
Re: if your LO takes one nap..
We're lucky if we can get 3 hours of a nap out of DD. Ever since about 5 months she has been a terrible napper. We've tried every time of day, undertired, overtired, just right tired, etc. I just resolved the fact that she's a bad napper and stopped stressing about it.
She has always slept 12 - 13 hours at night. That didn't really change when she stopped taking good naps.