I would suggest a course in the first instance Peter – your son may not like it and you don’t want to start buying all the gear straight away. I’ve made this mistake with my own kids in the past! There are courses all over the country so just search the internet for the closest one to you. The instructors will give him/you training on how to get started safely and what gear to buy if he wants to start forging at home. He may even learn how to forge his own tools so less for you to buy! Happy blacksmithing!
I too suggest having a proper introduction, however a cheap charcoal forge and a hammer and some scrap will soon tell you if they enjoy it or not, then you will know if its worth the added expense to go on a course 🙂
Its very addictive and im sure you will find the need to continue 🙂