Hi,
You have gotten some really good tips and advice above. What I would add is what an old blacksmith told me. "What a feller needs is TAA". Time at the anvil is what he was talking about. Not tools or fancy steels. Your young nephew is undoubtedly going to ruin a few pieces of steel as he learns. I would suggest that together you come up with some doable projects. Ways for him to succeed. Some rather simple things that will help him get in the several thousand hammer blows that it will take to teach him how to hit what he wants to hit and sharpen his eye. A cheap Harbor Freight hammer will work just fine to start. He can learn to dress the faces properly and how to see the small things that make for success. Later, after he understands a few things about smithing, he will "know" what he wants "his" hammer to look/feel like. Going to events and hooking up with a blacksmithing association will add immensely to his education and broaden his base. Have fun. I just "touched up/refurbished" a fireplace poker for my daughter that I made for my Mom 57 years ago. This time I put my mark on it. Sometimes things kind of stick with a person.