If everyone involved is a US citizen, this year's gift tax exemption is $17000 per recipient. That means you can give up to $34K written as $17K checks to each parent with no fuss.
You and your spouse can each give that amount, which doubles the number if you are married. Also if you go over, you need to file a gift tax form, but you would simply be eating into your lifetime exemption, which several million dollars before you need to pay an estate tax.