Your parents - in common with all others - think you are maturing when you sink cash into the purchase of a residence.
They are so anxious, they will borrow on your behalf.
If your folk are under 65, and they own their own house, they can borrow on 'equity release' and gift you the cash. These loans are repayable like any other loan, but the parents often dont make formal arrangements to get the gift repaid.
The Revenue have to accept the 'gift' approach, but are clear that if the additional borrowings are to be repaid by the child, they seem to think that then you may not be a first time buyer.
Gifting is totally legitimate, so dont get hyped about it. Obviously the 100% mortgage is an alternative.