Our son has flash cards on a key ring. He loves to sit with me and go through them - we have the letters of the alphabet, colors and shapes.
We really just go through them all as a game and he plays with them as a toy - it is not "learning" time as we let him decide whether or not he wants to go through them. His twin sister has no interest - she will sit as we read books together but she has no interest in going through the cards. She is much more into "pretend" play with dolls.
I would present them all - he is going to zoom in on certain ones and in time will expand his knowledge.