I think it really depends. I have borrowed from my parents, once, to buy a piece of property. I had almost all of the money, but I was living in Japan at the time (20 years ago) and my money was in Japan. I asked dad if I could borrow something like $40k...a very big sum for him, and me, at the time. But, when I did, I came to him with the proposal including a repayment schedule and interest, in hand. I knew the market rates, I knew what he was getting on CDs (that's still where they have all their money, believe it or not). He said he would check if he had any roll-overs coming, he did, and then agreed to lend it to me. We scheduled the closing right after the CDs rolled so that he could fund the deal when the property closed. The deal was that I would refund the majority as soon as I got to Japan, and had a year to repay the rest. I had it all paid off, including a year's worth of interest, in about 3 months. Good deal for him, good deal for me.
When your kid (OP) came to you asking for help, did he have a plan with him to repay? Was he offering interest? Or expecting a handout? Also, what are the considerations for leaving something to him upon your "departure"? (I ask that because we are hoping to leave our kids a substantial amount, but we are not telling them that. On the other hand, if death taxes are going to take away substantial amounts of what I have worked so hard to save, I won't mind transferring some of it early in the form of "help" here and there...not so much that it becomes a normal part of everyday life for them or "expected" as in "where's my allowance?" type of feelings, but a boost when a down payment is needed on a house, tuition help for grandkids, etc.
Bottom line is that while all the suggestions here provide food for thought, none of us know your situation like you do, and thus we may be miles off the mark. Listen to your intuition, and you'll be fine.
R