I have a super cool way of not even bothering memorizing it.
Depending on your peds clerkship exam (shelf vs. in-house), you may need to know some of this stuff.
I've never seen a question remotely close to asking about what stage of development a child is in.
The closest thing is a clinical vignette with a bunch of historical points and physical findings that has "Normal childhood development" or "Normal childhood behavior" as a possible choice.