I would start putting them in his hand and telling him or directing him where they go. even if they are not perfect.. he will begin to get the idea. He is not too young to help pick them up. Or if he likes putting things in a bigger thing.. get a small tote that he can put them into. We bought a blue tote from Walmart that is a cube with handles and a cover that has a circlular hole in the top for my daughter.. and made a game of picking legos up and putting them in the hole. Now it holds all her LeapFrog items in it.
If you make a game of it.. he will want to "play" So sing a little song.. we have one that goes.. pick up, pick up, eveybody pick up...and we add different words to it depending on what we are picking up.. Its something we made up.. and the kids, especially my 6 year old still sings it sometimes...
Its just something we started with the kids were young.. we made it fun and sang and played the pick up game.
It helped with mine... Hope it does with yours.
Hope that helps some.
W. in Watkins Glen
Mom to 3 kids
Korey-Mikel 16, Whitney 13 and Andrea 6