Within the standard big developments--picking up language and
movement and such--we see the oddest little developments. A few weeks
ago, Pete started asking about things he saw by saying waving his hands
excitedly, drawing his breath in sharply, and saying "Oooh! What
HAPPENED what they ARE?" The same phrasing would apply for
singular or plural referents, and often remarkably unexciting ones--for
one of many examples, we were walking downtown and had this exchange:
Pete: Oooh! What HAPPENED what they ARE?
Erik: Well, that's a door.
This kind of conversation happened all the time for about ten days,
and poof, no more.