Great start, a few things.
Your son, or anyone for that matter cannot contribute any more than they earned in taxable income in a year up to whatever the limit is, now $5.5k if you're under 50. IE, if "he" wants to contribute $5.5kthen he would need to earn at least that much. Essentially I am telling you that your son cannot have any contributions until he can earn an income. As you own your own business, you have some creative options available to you. IE, once he is legally able to work and have a reportable income, you could pay your son $5.5k for an hour of work as a 1099 contractor if you so desire, which you could then write off of your taxes as a business expense. Your son, could then in turn contribute the $5.5k to his IRA. Your son is responsible for paying the taxes on this income, however if this were his only income he effectively wouldn't have any, while you would writeoff the $5.5k as a business expense reducing your taxes payable by ($5.5k * your effective tax rate)
Booyah.
Now. as far as my opinion... As others have said, you need to take care of your own retirement needs first. Think of it like an air emergency... You need to secure your own mask first before helping others...
remember, due to health concerns, technology, etc you might not be able to work forever even though you'd like to.
Now, if you have taken care of yourself you next priority IMHO should be saving for his education, which you should use a 529 account for. (Tax advantaged education saving, similar to an IRA)
After that, then consider setting aside and investing some "slush" fund money for him.
My opinion is that is the order of precedent you should take.
After that, we could get into the specifics of investing - to keep a long and complicated discussion short, most people with a long time horizon (10+ years) would be best suited buying the vanguard S&P 500 index fund. Buy the same dollar allotment every year up or down, unless the market is tanking in which case buy double or triple the standard annual dollar allotment. Dollar cost averaging is your friend. Inspite of what any asshole tells you, it is the best simple investment you can make. In fact, the majority of paid money managers fall far short of the annual returns you will make with this strategy.