Small clothing closet

I would put in floating shelves: http://www.desertdomicile.com/2012/09/diy-15-chunky-wooden-floating-shelves.html?m=1

You could add a second rod right under the one that's there or build wood shelving. You could put in wire shelving or look for wire shelving that will fit the space. Don't forget to add baskets or boxes in the bottom for various things.

We have put in bookcases with baskets under the rod. You can hang another rod off existing rod.

Install sturdy shelves and use baskets instead of drawers for toys or clothes. Keep accessible things on the bottom for him.

Try adding a second rod a tension style rod. Add a wood shelf over the top of the first rod and Home Depot will cut the wood for you. Add plastic drawer storage carts for Walmart or family dollar and if you want get fancy spray paint those and wall paper the back of the closet in boys colors or theme. If your not liking the plastic carts try lower shelfs of baskets.

Purchase some of the plastic 3 or 4 drawer plastic units sold at Big Lots, Walmart, etc. I would also install extra hooks or shelves to make the most of the space. Another option is underbed storage for out of season clothes.

We also had a very small closest in my child's bedroom. We had a rod for hanging, with a hanging purse container which held jeans, sweaters/sweats, tees, socks and underpants. Shoes went into a basket on the floor. Winter/summer clothing went into boxes on the upper shelf.

Don't forget that children are constantly growing. Whatever you choose, make it strong, but temporary enough so that when it is outgrown, you can repurpose the space without too much cost and effort.

you could always lift the top rod and put a second rod on the bottom.