Saving strategy for kids first home in Greater Toronto

I am in my mid 40's living in central Toronto. I have two kids aged 7 and 10.

I consider ourselves middle-upper household income. RESP, TFSA, RRSP are in relatively good shape. I just invest in for the long term with S&P500 and Nasdaq linked ETFs.

We are moderately frugal.

I have been trying to mold my mindsight and develop some sense of saving for kids for their first property when they get to their mid 20s. Specifically that down payment.

assumptions:
1) They have a "good paying" job enough to cover property carrying costs.
2) I would be willing to give most of our TFSAs.
3) RRSP portfolio is sufficient for modest frugal retirement for me and my wife.
4) I will start contributing to their TFSAs at age 18 it will be theirs with the expectation that use it for first home down payment.
5) 15 years out, it seems like a 20% down payment will have to be $300-500K for a decent condo. This is just off the top estimate. Seems crazy.
6) I plan to have them financially educated in terms of understanding the concept of managing, investing and psychological aspects (e.g. risk/rewards/timing market) so that they can rely proper wealth manage than just trying to make as much money from a job.

I know this is a very big 'it depends' type of question. It also depends on culture. Just want to gather other people's perspective and mind sight. I read other reddit posts where young professionals and young couples with very decent incomes feel like it is out of reach to have the traditional lifestyle of a comfortable home in around the city, while having 2 kids to raise.

I think for me, right now I am trying to have a better sense of perspective, mindsight and values. And then financially model out various scenarios and projections in my spreadsheet.