At 18 months my previously crap sleeper started sleeping through (mostly) but swapped multiple night wakings for waking very, very early - 5-530 generally.
This lasted for around a year. Then he dropped his nap and sort of shifted that sleep to the morning. Gradually he’s been waking later and later and now sometimes I have to wake him. (Not often.)
I have a ‘new’ 18 month old who thankfully doesn’t seem as inclined to start the day when it’s still the middle of the night but she did just wake me about half an hour ago and I am waiting for her to go back to sleep.
But - AIBU to be horrified this was a habitual start time if you like for me once upon a time? I’ve given myself such a hard time about not properly enjoying ds as a toddler but I kind of think no wonder; I must have been sick with exhaustion!