Hi OP,
My husband was largely (90%) given a flat by his parents (they gave each of their children a flat that they already owned- DH's was a bit more expensive than his siblings' so he got a mortgage for the difference.
My brother was given a flat by our parents, and they gave much smaller cash gifts to two sisters and me. Totally fine and didn't cause any bad feeling- we're all financially secure and my brother is a bit younger so by the time he was ready to own his own place prices had skyrocketed.
It's all been fine. Nobody lost their drive- I think the amount of drive and ambition you have are largely down to your character rather than whether you have secure housing. In the current climate I think not helping children with this stuff when you can is really misguided- maybe it would have been different 30 years ago but where we live a small starter flat costs £500k+. It's not character building to have to strive for something like that, it's depressing, and also means people make career choices that are focused too much just on money.
I also find it slightly depressing how many people on this thread seem to equate "losing ambition" with "not being purely money focused". One of the joys of a financially secure background is that you can follow passions and take risks- of course sometimes that means the risks don't work out. That's a good thing in my book. I would hate to feel that the lesson I was giving my kids was "focus just on money, work very hard at something conventional, then with lots of time and some luck you may be able to buy a home, something that in a better functioning society would be readily affordable to all". This is one of the many reasons why people from richer backgrounds are over-represented in riskier careers (like acting or writing- one might add obscure academic disciplines).
All our financial planning is based on the fact that we'll be buying flats for our kids when they are ready and we have a large sum earmarked for this, given that they may want to stay in this area. I might mention the concept of marital assets to them one day as I doubt they know much about divorce law but probably separately to giving the gifts- I would hate them to feel that they were duty-bound to keep the asset in the family and therefore to stay in an unhappy marriage. It's a gift. If you can't afford to give it freely then better to work out another arrangement.
I feel a lot of responses on this thread come from a poverty mindset (not that the people posting are in poverty, but that their concern is always "not enough"- not enough money, not enough ambition, not enough security, not enough happiness). I'm not sure that that is the best way of thinking when in fact there is enough. I'm also not sure that it's the mindset that necessarily leads to plenty, quite the reverse in fact.