That is very individualized as a lot depends upon how much exposure that child has had to one on one learning. Of course a child who has been read to daily, had much encouragement to talk , explore and be nurtured is probably going to do much better than one who has not. At two, every single month makes a difference so you are going to see a lot of variation between a 24 month old and a 30 month old. Some two year old children will have a large vocabulary and know their ABC's by sight at 2 1/2. Other couldn't tell you at 5. If you are speaking of recalling a person or a name, a child at 2 is going to need many exposures to remember that name . Traumatic events will affect how a child meets later challenges, but they usually can't remember specifics that aren't reinforced by repetition.