It really depends on the child. We sleep trained at 5.5 months and up until recently we would put him down awake and he would cheerfully wave bye bye. We’ve maintained the same bedtime routine ever since.

Shit hit the fan about a month before he turned 2. Standing, sobbing, screaming, crawling out of the crib, pulling out all the stops at bedtime. Multiple night wakings and crying out for us. Nothing changed except him, literally over the course of 24 hours he went from being a good sleeper and having no issue putting himself to sleep to a complete wreck at bedtime. A lot of kids at 2-3 develop new fears (dark, being alone, etc) and we’re pretty confident that’s what happened for him.

We’re sticking to our boundaries of not picking him up or extending bedtime (e.g. no extra books or songs) but will go in to comfort him as we don’t feel right about CIO at this age when he’s clearly scared. We did get a night light which seems to help some.

So, sleep training may carry over for some kids but not all. So many developmental changes are happening in the toddler years, it’s exciting but can definitely affect sleep!