When you gift them the property it becomes their property. Which means if they become ill they will have to use those assets before they are eligible for Medicaid.
You can gift anything you want. If the IRS detects that you did it to avoid taxes, they will not allow the tax advantage.
If you gift it with conditions: they can't sell it, or donate it, or give it to somebody else in their will; then the transaction is a sham.
If you give it and then 5 years later your parents have to go into a long term care center, and they start to run out of money, the government will require them to be broke before they can have their care paid by Medicare. Telling the government that you are holding it for their child will not prevent them from having to sell it.