How’s about working smart?
If I had a child that was ready to move out and had the funds to help them, the smart thing to do is to help them.
The value of the house should out pace inflation and any interest rates that the bank can offer by just having the money sit there.
Say you lent 10% to your child, you could just say I want 10% of the house sale when they move. Even if you don’t expect or want it back, I’m sure the 10% is well worth it when your child looks after you when your in retirement, with the raising cost of home care.
For my first house purchase, I saved 5%, my brother borrowed me 2.5% all paid back in 3 years, which helped with his kids wedding costs, my mum and dad gave me 2.5%, which is much more useful then than giving me it when/once they past away.
It’s not just the house deposit that a first time buyer has to save for, I was kinda lucky as I was already renting and had most of my furniture but still had to pay for central heating to be fitted, a bed to sleep in as my old one was rotten, etc etc… let’s not forget the cost of all the paperwork.