A couple things to consider.
Gift tax - if you just give them the money, they may be subject to the gift tax for anything above $15k per person. You can avoid this by offering the loan.
Loan interest #1 - You'll be required to pay taxes on the interest of the loan. Not a big deal. Just be aware that you're required to report it.
Loan interest #2 - You'll need to issue the loan at the market interest rate at that time. If you give them a discounted interest rate, they will still be required to pay the taxes on the amount you discounted. This is a range because interest rates are charged on credit worthiness. Just stay away from an abnormally low interest rate and you should be fine. If you go too low, you can peak the IRS interest in your finances.
What are you going to do if they don't make a payment or pay consistently late? I know it's your parents. I'm sure they are wonderful people. As an advisor I've see deal like this that had the best of intentions, ruin relationships. If I were you, I'd have a very straight forward and blunt conversation about your expectations followed by a note that's been reviewed by a lawyer and includes the conditions, upon which you both agreed.
I hope that last part didn't come across as condescending.
Great job having the means to help your parents out even if it's temporary! That's what it's all about!