My three year old son. Has a pretty good memory. (Sometimes better than mine). And will happily talk about and answer questions about things that we have done. But he just places it all 'last year'. Even if I explain the concepts of yesterday, last week, etc. When asked when something was it always seems to be last year.
He also seems to have difficulty remembering events in order. Nit being sure if something yesterday and last year happened more recently.
If this is just a concept that will come in time then I don't mind letting him work it out.
However if nor is there anything I can do to help him understand the concepts? A game or something?