"In" and "up" don't strike me as especially odd...but if he's using words like "and" and "the" and "at" I wonder how they can be meaningful when they are used without nouns? Also, I'm not sure what you mean by "re-enforce" in this context. I don't know what most parents do, but I didn't go around making a big deal out of any particular word when DD was a baby. I just talked to her. But then, she wasn't a terribly early talker.