re: 18 year old son wants to start building credit. Recommendations?

As said by a few, I'll either just add him to one of my cards or co-sign a loan for him.

I have an old credit union account and I called them to see what they might have as well. They have a "credit builder" loan that he can take out. He'll never see the money for the term of the loan (example is $1k) but he'll make monthly payments on it. At the end of the term he'll get the loan money plus any accrued interest on it. Kind of like a forced savings account that he can't touch, but has to pay the payments.